Zoo Biology 17:123–134 (1998)

© 1998 Wiley-Liss, Inc.

Nutrient Composition of SelectedWhole InvertebratesDayna Barker, 1 Marianne P. Fitzpatrick, 2* and Ellen S. Dierenfeld 2

1Department of Biology, Manhattan College/College of Mount Saint Vincent, Riverdale,New York

2Department of Nutrition, Wildlife Conservation Society, Bronx, New York

Although nutrient requirements of insectivores have not been specifically deter-mined, detailed chemical analysis of invertebrates used in zoo feeding programsis essential for evaluating nutritional adequacy based on domestic animal mod-els. Additionally, such data can provide valuable suggestions for future researchpriorities. Proximate composition, fat-soluble vitamins, and minerals in meal-worms (Tenebrio molitor and Zophobas morio), crickets (Acheta domesticus),waxworms (Galleria mellonella), fruit flies (Drosophila melanogaster), and earth-worms (Lumbricus terrestris) were determined. All species had a water con-tent >50% of their body weights. Larval invertebrates had higher fat content(x > 30% dry matter [DM]) than adult species. Total nitrogen (N) rangedfrom 5.2±1.1% DM (earthworms) to 10.3±0.4% DM (adult crickets), whereaschemically bound N comprised 3–10% of total N in all invertebrates. Neutraldetergent fiber, used as a measure of chitin, averaged 15.3±3.6% DM for allspecies except wild-caught earthworms, which were higher (51% DM). VitaminE concentrations ranged from 15±3 IU/kg DM (mealworms) to 509±232 IU/kgDM (waxworms). Vitamin A concentrations were undetectable (fruit flies) to lowin all samples; none met the recommended dietary vitamin A concentrations es-tablished for domestic carnivores. Insects had low calcium concentrations (x =0.11%) and imbalanced calcium:phosphorus ratios except for pinhead crickets.Insects sampled contained sufficient concentrations of Cu, Fe, Mg, P, and Zn tomeet known requirements of domestic birds and mammals, whereas super-mealworms and waxworms contained deficient levels of Mn. Earthworms ap-peared to meet dietary mineral requirements, based on domestic bird and mammalrecommendations. Zoo Biol 17:123–134, 1998.© 1998 Wiley-Liss, Inc.

Key words: invertebrates; animal nutrition; vitamins; minerals; proximate composition

INTRODUCTION

Invertebrates comprise a large portion of the diets of many species maintainedin captivity. Diets are normally based on field observations of feeding behaviors,

*Correspondence to: Marianne P. Fitzpatrick, Animal Health Center, 185th St. & Southern Blvd., Bronx,NY 10460. email: mfitzpatrick@wcs.org

Received for publication August 4, 1997; revision accepted December 9, 1997

124 Barker et al.

with little detail concerning chemical composition. Although the behavioral aspectsof feeding should not be ignored, it is important to consider nutritional compositionin formulating and evaluating diets.

Most of the literature concerning the nutrient composition of invertebrates usedin zoo feeding programs has focused on mineral content, specifically on calcium:phosphorus ratios [Jones et al., 1972; Martin et al., 1976; Allen, 1983; Trusk andCrissey, 1987]. The mineral requirements of the house cricket (Acheta domesticus)have been presented [McFarlane, 1991], and a few studies summarized the mineralcontent of various insect species [Levy and Cromroy, 1973; Studier and Sevick, 1992]as well as individual species such as June beetles (Phyllophaga rugosa) [Keeler andStudier, 1992] and the eastern tent moth (Malacosoma americanum) [Studier et al.,1991]. Other authors discussed proximate composition [Martin et al., 1976; Redfordand Dorea, 1984; Pennino et al., 1991], but few analyzed fat-soluble vitamin con-centrations [Bowers and McCay, 1940; Nestler et al., 1949; Pennino et al., 1991]with regard to insectivore nutrition. This report attempts to provide a more compre-hensive summary of the nutritional content of selected whole invertebrates that canbe used to evaluate the diets of animals maintained in zoological parks or in othercaptive situations.

MATERIALS AND METHODSCollection of Specimens

Mealworms from the family Tenebrionidae (Tenebrio molitor [~160 mm and320 mm length—Mighty Mealys™] and one size of Zophobas morio—super-mealworm), crickets (Acheta domesticus, juvenile and adult), waxworms (Galleriamellonella), and earthworms (Lumbricus terrestris) were purchased from commer-cial suppliers (Mighty MealysTM and waxworms: Grubco Inc., Hamilton, OH; meal-worms and supermealworms: Rainbow Mealworms, Compton, CA; crickets: Top HatCricket Farm, Kalamazoo, MI; earthworms: Michael’s Wholesale Bait, W. Spring-field, MA,). Earthworms were also wild-caught in Westchester County and in theBronx, NY. Earthworms were identified presumptuously by Dr. Pirone of ManhattanCollege (pers. comm). Fruit flies, Drosophila melanogaster, were raised at the Worldof Birds, Wildlife Conservation Park, Bronx, NY, using Instant Drosophila Medium(Carolina Biological, Burlington, NC). The average lengths and masses for the vari-ous invertebrates sampled, as well as the diets and/or substrates on which they wereraised, are found in Table 1.

All samples were live-frozen at –20°C and partially thawed at room tempera-ture prior to analysis. Whole specimens were ground using a small food processor(Hamilton Beach Food Chopper) and vitamin assays were performed immediatelyafter extraction. Remaining subsamples were freeze-dried and ground, using a labo-ratory mill, prior to fat, protein, fiber, and mineral analyses.

Proximate Composition

The percentages of moisture, ash, crude fat, and total nitrogen were obtainedfor all samples using AOAC methodology for meat [Ellis, 1984]. Duplicate samples(≥0.5 g) were weighed, freeze-dried, and the percentage of moisture was calculated.These samples were then incinerated in a Thermolyne muffle furnace at 550°C over-

Nutrients in Whole Invertebrates 125

night and total ash was calculated. Crude fat was determined by extraction with pe-troleum ether using the AOAC Official method 991.36 [1996]. Total nitrogen wasdetermined using a macro-Kjeldahl method with a copper catalyst. Acid detergentfiber nitrogen (ADF-N), a measure of chemically bound nitrogen, was analyzed us-ing acid detergent fiber methods described by Conklin [1987]. Samples were boiledin an acid detergent solution for 1 hr, filtered (Whatman paper # 54) and rinsedthoroughly with water, and the filtrate was subjected to Kjeldahl analysis. Chitin wasdetermined by modified methods of Stelmock et al. [1985] using neutral detergentfiber (NDF) instead of acid (ADF) as the measure of complex carbohydrates.

Fat-Soluble Vitamins

Vitamins A and E were analyzed using a modification of the methods of Tayloret al. [1976]. Duplicate tissue samples (≥0.5 g) were homogenized with 5 ml of 2mM EDTA and 1 ml of 25% sodium ascorbate solution. The samples were mixedwith 4 ml of 95% ethanol and 1 ml of 50% KOH. The mixtures were saponified byheating in a 70°C water bath for 15 min, then cooled in an ice bath. Fat-solublevitamins were extracted with 1 ml hexane containing 0.2% BHT, and a 1 ml aliquotof the hexane layer was evaporated under nitrogen. Saponification, extraction, andevaporation procedures were performed under yellow light. Samples were then re-constituted with 0.25 ml ethanol containing 0.1% BHT. A Perkin Elmer (PE) series400 liquid chromatograph equipped with a 15-cm C-18 reversed-phase column wasused to quantify α-, γ-, and δ- tocopherols, and retinol as measures of vitamins E

TABLE 1. Body masses and lengths (x ± SD) of various invertebrate species used in feedingprograms of the Wildlife Conservation Society (sample size in parentheses)

Species Mass (g) Length (cm) Diet/substrate

MealwormMealworm (12) 0.1 ± 0.0a 1.6 ± 0.2a Wheat, grain, carrotsTenebrio molitorMighty MealysTM (12) 0.4 ± 0.1b 3.2 ± 0.2b Wheat bran,Tenebrio molitor unknown supplementsSupermealworm (12) 0.6 ± 0.1b 3.2 ± 0.3c Wheat, grain, carrotsZophobas morio

Crickets*Acheta domesticus 0.2 ± 0.0a 2.1 ± 0.2a (Identical for both):Adult (12) corn meal, wheat midds,

soy bean hulls, meat meal,molasses, fish meal

Juvenile (20) <0.01b 0.2 ± 0.1b Shipped with raw potatoWaxworms (12) 0.3 ± 0.1 2.0 ± 0.2 None

Galleria mellonellaFruit fly (20) <0.01 0.2 ± 0.1 Carolina Biological Instant

Drosophila melanogaster Drosophila Medium (plain)Earthworms

Lumbricus terrestrisWild-caught (23) 1.1 ± 0.7a 8.2 ± 3.1a

Commercial (17) 2.9 ± 1.1b 14.7 ± 4.9b Peat humus soil

*All cricket information adapted from Barker [1997].Mealworms, crickets, and earthworms with different superscripts are significantlydifferent (P ≤ 0.05) within each group.

126 Barker et al.

and A, respectively. The mobile phase was 96:4 methanol:water for tocopherol de-tection, and 90:10 methanol:water for retinol separation at a flow rate of 2 ml/min.Tocopherols were measured with a PE LS-1 fluorescence detector (excitation wave-length = 280 nm; emission wavelength > 310 nm) and retinol was monitored at 325nm on a PE model LC-95 spectrophotometer. External standards were compared tosample extracts for determination of vitamin concentrations. Vitamin E activity wascalculated as 1 mg α-tocopherol = 1.49 IU; 1 mg γ-tocopherol = 0.15 IU; 1 mg δ-tocopherol = 0.05 IU [Horwitt, 1993]. Vitamin A activity was calculated as 0.3 µgretinol = 1 IU [Olson, 1984].

Elemental Composition

Tissues were prepared for mineral analysis using standard methods [PerkinElmer, 1982]. Ashed samples were dissolved in 3 ml 3N HCl with heat then dilutedto 25 ml with a 1% La solution. When necessary, samples were further diluted with0.36 N HCl containing 1% La. Calcium, Cu, Fe, Mg, Mn, and Zn were run sepa-rately on a PE atomic absorption spectrophotometer (Model 3100) with an air-acety-lene gas mixture and a 0.36 N HCl with 1% La blank. Phosphorus was measuredusing modified AOAC colorimetric methods [Cunniff, 1996].

Statistical Analyses

Data are reported as means ± standard deviation. Differences among means withineach group were determined by unpaired t-tests (earthworms, crickets) or analysis ofvariance (mealworms), with the LSD value calculated as a Tukey statistic at P = 0.05[Snedecor and Cochran, 1967], using Systat computer software [Wilkinson, 1987].

RESULTS AND DISCUSSION

Proximate Chemical Composition

The proximate chemical composition of invertebrates is presented in Table 2.Mealworms had significantly higher water (P < 0.01), lower crude fat (P < 0.001),and higher ADF-N (P < 0.05) concentrations than Mighty MealysTM and super-mealworms. Additionally, total nitrogen and ash contents were higher in regular meal-worms compared with the larger-sized specialty mealworms. Significant differencesin both crude fat (P < 0.001) and total nitrogen (P < 0.01) were found between adultand juvenile crickets [see also Barker, 1997]. Differences in wild-caught comparedwith commercially supplied earthworms of the same species were seen in crude fat(P < 0.05), total nitrogen (P < 0.01), chitin (P < 0.001), and ash (P < 0.01) content.These differences might be due to differences in substrate (hence diet) between thetwo worm samples, with the wild-caught worms consuming soils containing muchhigher plant fiber (organic) and inorganic matter. The commercial earthworms wereraised on peat humus soil, which has been shown to have a higher nitrogen contentthan other soils [Brady, 1974].

Crude fat varied greatly among the invertebrate species sampled, likely due toundocumented differences in reproductive states, season, age/life stage, or sex [Myersand Pedigo, 1977; Redford and Dorea, 1984; Mason et al., 1990; Pennino et al.,1991]. Larval insects (mealworms and waxworms) had the highest fat content. Redfordand Dorea [1984] reported that termite and ant alates, as well as larval stages of

Nutrients in Whole Invertebrates 127

other species, contained more fat than adults. Mealworm and waxworm values re-viewed in that study were 33 and 62% fat (dry matter [DM] basis), respectively. Bycontrast, in this study, the nymph stage of the cricket contained a lower fat contentthan adults. Fats have a higher caloric content (9 kcal/g) than proteins (4 kcal/g) orcarbohydrates (4 kcal/g), thus providing a more concentrated energy source. In addi-tion, the oxidation of fats yields twice the metabolic water of carbohydrates [Downerand Matthews, 1976] and may provide a dietary source of water for those animalsconsuming mainly larvae.

Supermealworms contained significantly less nitrogen than mealworms andMighty MealysTM. Studier et al. [1991] attributed the lower nitrogen content found inlarger caterpillars to decreases in the surface area to mass ratio accompanying growth,since significant amounts of nitrogen are contained within the exoskeleton.Supermealworms are the largest of the three mealworms measured here, which mayaccount for their lower nitrogen level. Only 5-6% of total nitrogen was measured asADF-N (chitin-bound nitrogen) in the three mealworms in this report. Additionally,

TABLE 2. Proximate nutrient composition (x– ± SD) of various invertebrate species used infeeding programs of the Wildlife Conservation Society (sample size in parentheses)

% Dry Matter

Water Crude TotalSpecies (%) fat nitrogen ADF-N NDF Ash

MealwormsMealworm (6) 62.9a 31.1a 8.3a 0.5a 14.5 4.3a

Tenebrio molitor ± 3.6 ± 3.9 ± 0.9 ± 0.1 ± 2.9 ± 3.7Mighty MealysTM (6) 58.3b 40.3b 7.7a 0.4b 11.2 3.2b

Tenebrio molitor ± 0.6 ± 0.7 ± 0.1 ± 0.0 ± 0.8 ± 0.7Supermealworm (6) 57.0b 40.8b 6.9b 0.4b 13.0 3.5ab

Zophobas morio ± 1.4 ± 2.3 ± 0.2 ± 0.1 ± 6.8 ± 0.6Crickets*

Acheta domesticusAdult (6) 73.2 22.8a 10.3a 0.7 19.1 5.1

± 1.9 ± 1.5 ± 0.4 ± 0.1 ± 2.5 ± 1.4Juvenile (10) 66.8 9.8b 8.8b 0.6 16.4 9.1

± 9.8 ± 1.4 ± 0.5 ± 0.1 ± 5.6 ± 6.7Waxworm (6) 61.9 51.4 6.6 0.4 12.1 3.3

Galleria mellonella ± 2.1 ± 5.4 ± 0.4 ± 0.1 ± 3.8 ± 1.0Fruit fly (4) 67.1 17.9 9.0 1.0 16.2 5.2

Drosophila melanogaster ± 3.5 ± 3.0 ± 0.1 ± 0.3 ± 1.5 ± 0.7Earthworms

Lumbricus terrestrisWild-caught (6) 74.5 12.6a 5.2a 0.2 51.2a 45.7a

± 2.0 ± 1.0 ± 1.1 ± 0.1 ± 6.3 ± 6.6Commercial (6) 75.8 10.6b 8.1b 0.3 20.9b 24.9b

± 4.8 ± 1.7 ± 1.5 ± 0.1 ± 13.2 ± 11.4

*All cricket information adapted from Barker [1997].Mealworm and earthworm classes with different superscripts are significantly different (P ≤ 0.05)within groups.

128 Barker et al.

the crickets did not appear to follow this suggested pattern; ADF-N in both cricketstages comprised 7% of total nitrogen.

Invertebrates were previously documented as an excellent source of dietarynitrogen [Martin et al., 1976; DeFoliart et al., 1982; Frye and Calvert, 1989]. Thenitrogen values from 16 orders of flying insects ranged from 13% DM in Megalopterato 19% DM in Hemiptera [Studier and Sevick, 1992]. The eastern tent moth wasreported to have nitrogen values ranging from 11% DM in pupae to 23% in cocoons[Studier et al., 1991]. Our values are more comparable to the Redford and Dorea[1984] review, with nitrogen values ranging from 1.2% DM in an ant species to14.7% DM in bees. However, estimates of protein content (calculated as nitrogen ×6.25) may be misleading. Some of the nitrogen is contained within the N-acetylglucosamine subunit of the chitin polymer and may be unavailable to insecti-vores [Finke et al., 1989]. This protein value may be corrected by subtracting theADF-N (or nonprotein nitrogen) from the total nitrogen before multiplying by 6.25.The corrected protein values range from 31% (wild-caught earthworms) to 60% DM(adult crickets) in our samples, indicating that these species appear to contain ad-equate quantities of protein, but that does not guarantee that they provide a balancedprotein source for animals consuming them. Specific amino acid composition hasnot been detailed for most invertebrates (only Jones et al. [1972] and Oyarzun et al.[1996] list amino acids found in mealworms and termites, respectively), and needsto be evaluated in more detail.

NDF, a measure of dietary fiber (both chitin and cell wall constituents of plants),made up ~15% of DM in most samples, similar to previously reported values [Penninoet al., 1991]. No significant difference in NDF concentration was detected amongvarious sizes or species of mealworms, averaging 12.9% of DM. Earthworms con-tained higher NDF levels than other samples, which probably reflects cell wall car-bohydrates of gut contents rather than chitin per se. The difference in NDF betweenwild-caught and commercial earthworms of the same species may be due to the dif-ferences in their substrate composition. Likewise, four species of dung beetles(Catharsius surealiatus, Kheper aegyptiorum, Heliocopris amatnadeus, and one un-known species) had an average NDF of 49% [Dierenfeld, unpublished data], whichis probably indicative of their gut contents. Chitin may be a significant energy sourcein diets of animals possessing chitinase [Cornelius et al., 1976]; small mammalswere reported to digest as much as 20% of chitin [Allen and Oftedal, 1989; Graffamet al., in press]. For those animals lacking chitinase, this indigestible component maybe important to gut function and nutrient absorption [Van Soest, 1994].

Ash values, a measure of inorganic (mineral) content, were generally low(<10%), as previously reported [Martin et al., 1976; Redford and Dorea, 1984; Penninoet al., 1991]. Crickets contained more ash than other insects, and the variable ashcontent of juvenile crickets deserves further detailed investigation. The higher ash con-tent of the earthworms is most likely due to soil ingestion; likewise, the different ashvalues for commercial and wild-caught earthworms of the same species may be due todifferences in soil composition, although substrates were not analyzed in this study.

Vitamin Concentrations

Table 3 shows the calculated vitamin A and E concentrations (IU/kg DM) quan-tified in whole invertebrates. Vitamin E content in mealworms can be altered by diet[Pennino et al., 1991], and suitability of diet and/or substrate used in producing meal-

Nutrients in Whole Invertebrates 129

worms for managed feeding programs warrants detailed investigation. Significantdifferences detected between both vitamin E (P < 0.001) and vitamin A (P < 0.01)concentrations in mealworms are most likely due to differences in vitamin content ofdiets fed by commercial suppliers rather than species or size. The significant differ-ences in vitamins E and A between wild-caught and commercially obtained earth-worms (P < 0.01 and P < 0.001, respectively) may reflect substrate (dietary)differences.

Fat-soluble vitamin requirements have not been determined for most exoticspecies. However, vitamin E requirements established for domestic mammalian car-nivores range from 20 to 80 IU/kg on a dry basis [NRC, 1982, 1985, 1986]. Mostinvertebrates sampled contained vitamin E levels within this range with the excep-tion of Mighty MealysTM (15.0 IU/kg). Vitamin E deficiencies have been recognizedin a number of zoo species [Dierenfeld, 1989] but have not been documented ininsectivores per se.

The vitamin A concentrations in invertebrates sampled ranged from undetect-able in fruit flies to 2,400±279 IU/kg in wild-caught earthworms. Vitamin A require-ments established for wildlife and domestic carnivores range from ~6000 to 15,000IU/kg DM [NRC, 1982, 1985, 1986; Robbins, 1993]. All samples fell below thisrange, indicating that insects and earthworms may be a limited dietary source of

TABLE 3. Fat soluble vitamins (Vitamins A & E; x– ± SD; DM basis) in whole invertebrates usedin feeding programs of the Wildlife Conservation Society (sample size in parentheses)

Species Vitamin E (IU/kg) Vitamin A (IU/kg)

MealwormsMealworm (6) 30 ± 3a 811 ± 324a†

Tenebrio molitorMighty MealysTM (6) 15 ± 3b 161 ± 91b

Tenebrio molitorSupermealworm (6) 32 ± 6a 972 ± 570a

Zophobas morioCrickets*

Acheta domesticusAdult (6) 81 ± 41 811 ± 849Juvenile (8) 71 ± 42 471 ± 585

Waxworm (6)Galleria mellonella 509 ± 232 150 ± 160

Fruit fly (4)Drosophila melanogaster 23 ± 13 Not detected

EarthwormsLumbricus terrestrisWild-caught (6) 70 ± 12a 2,400 ± 279a†

Commercial (6) 229 ± 82b 328 ± 171b†

*All cricket information adapted from Barker [1997].†Vitamin A values from Dierenfeld et al. [1995].Vitamin E activity = 1 mg α-tocopherol = 1.49 IU; 1 mg γ-tocopherol = 0.15 IU; 1 mg δ-tocopherol =0.05 IU [Horwitt, 1993].Vitamin A activity = 0.3 µg retinol = 1 IU [Olson, 1984].Mealworms and earthworms with different superscripts are significantly different (P < 0.05) withineach group.

130 Barker et al.

vitamin A, a fact previously documented by others [Bowers and McCay, 1940; Nestleret al., 1949; Jones et al., 1972; Martin et al., 1976; Pennino et al., 1991; Dierenfeldet al., 1995]. It may be possible that insectivores simply have a lower dietary needfor vitamin A [Annis, 1993] than other species. Several instances of apparent vita-min A toxicity have been noted in zoo animals [Dierenfeld et al., 1995], but nocontrolled studies have been conducted, particularly with insectivores.

Regarding vitamin A nutrition, the ability to convert carotenoid pigments toactive vitamin A has been previously documented in many species but has not yetbeen examined in insectivorous species. Carotenoids have been identified in crickets(n = 5) and waxworms (n = 3) (β-carotene, lutein, respectively) with possible vita-min A-precursor activity [Brush, 1990; Dierenfeld et al., 1995], whereas no caro-tenoids have been detected in mealworms (n = 1) or commercially obtainedearthworms (n = 2). Nestler et al. [1949] previously found carotenes in several her-bivorous invertebrates and one carnivorous insect, presumably obtained from dietaryingredients.

Elemental Composition

The mineral concentrations of invertebrates are presented in Table 4. Signifi-cant differences in Mg (P < 0.05), P (P < 0.001), Fe (P < 0.05), Mn (P < 0.01), and

TABLE 4. Selected macrominerals and trace elements (x– ± SD; DM basis) in whole invertebratesused in feeding programs of the Wildlife Conservation Society (sample size in parentheses)

Ca Mg P Cu Fe Mn ZnSpecies (%) (%) (%) (mg/kg) (mg/kg) (mg/kg) (mg/kg)

MealwormsMealworm (6) 0.12 0.28a 1.42a 17.77 39.70ab 6.79a 131.02a

Tenebrio molitor ± 0.09 ± 0.02 ± 0.15 ± 4.72 ± 19.21 ± 4.23 ± 6.81Mighty MealysTM (6) 0.03 0.22b 1.27a 14.94 25.85a 5.56a 82.84b

Tenebrio molitor ± 0.01 ± 0.01 ± 0.28 ± 1.53 ± 15.98 ± 0.19 ± 3.63Supermealworm (6) 0.12 0.18c 0.83b 13.94 50.34b 1.54b 87.50b

Zophobas morio ± 0.15 ± 0.02 ± 0.24 ± 3.06 ± 6.52 ± 0.63 ± 4.43Crickets*

Acheta domesticusAdult (6) 0.21 0.08a 0.78 8.50 112.33a 29.65a 186.36a

± 0.03 ± 0.01 ± 0.08 ± 1.01 ± 58.10 ± 4.54 ± 16.48Juvenile (8) 1.29 0.16b 0.79 9.61 196.80b 52.76b 159.06b

± 2.26 ± 0.04 ± 0.19 ± 1.74 ± 79.75 ± 17.83 ± 14.97Waxworm (5) 0.06 0.09 1.20 3.06 77.27 3.28 78.78

Galleria mellonella ± 0.01 ± 0.01 ± 0.11 ± 1.26 ± 13.06 ± 0.78 ± 5.72Fruit fly (4) 0.14 0.13 1.10 8.66 454.22 16.09 146.95

Drosophila melanogaster ± 0.22 ± 0.02 ± 0.05 ± 3.98 ± 50.91 ± 2.68 ± 71.05Earthworms

Lumbricus terrestrisWild-caught (6) 0.97 0.31a 0.79 32.86a 11,087.45a 199.40a 270.80

± 0.28 ± 0.03 ± 0.13 ± 17.88 ±2,938.07 ± 44.86 ± 88.94Commercial (6) 1.21 0.19b 0.86 8.09b 5,801.76b 113.13b 231.15

± 0.03 ± 0.03 ± 0.15 ± 1.66 ±2,323.50 ± 51.04 ± 55.54

*All cricket information adapted from Barker [1997].Mealworms, earthworms and crickets with different superscripts in columns are significantly different(P < 0.05) within each group.

Nutrients in Whole Invertebrates 131

Zn (P < 0.001) were seen among mealworm samples with no consistent pattern at-tributing these differences to body size, species, or even diet fed to the mealworms.Juvenile crickets contained more Mg (P < 0.001), Fe (P < 0.05), and Mn (P < 0.01)and less Zn (P < 0.01) than adults [see also Barker, 1997], even though both agegroups were fed an identical diet [Top Hat Cricket Farm, pers. comm.]. Wild-caughtearthworms had significantly higher Mg (P< 0.001), Cu (P < 0.01), Fe (P < 0.01),and Mn (P < 0.05) concentrations than those commercially obtained, presumablydue to soil and/or dietary substrate differences. Calcium requirements for birds andmammals range from 0.4 to 2.5% DM [Robbins, 1993]. None of the insects sampledmet these requirements, although the calcium levels of pinhead crickets were highand quite variable (0.05–6.90%) . Insects were previously reported as an inadequatecalcium source [Jones et al., 1972; Martin et al., 1976; Frye and Calvert, 1989; Frye,1991; Keeler and Studier, 1992; Allen et al., 1993], with the exception of stone flies(order Plecoptera) containing 1.2% Ca, DM basis [Studier and Sevick, 1992] andcocooning eastern tent moths at 1.8% Ca DM basis [Studier et al., 1991].

The phosphorus requirements for birds and mammals (0.3–0.6% DM) [Robbins,1993] should be met by all of the species analyzed in this study, simply based ontotal P content measured. Earlier studies showed inverse calcium:phosphorus ratiosin insects [Jones et al., 1972; Martin et al., 1976; Frye and Calvert, 1989; Frye,1991; Allen et al., 1993]. Calcium-to-phosphorus ratios of 1:1 to 2:1 are consideredappropriate for proper Ca and P absorption and metabolism in vertebrates; excessesof calcium have less effect than excess phosphorus on absorption [McDonald et al.,1973; Martin et al., 1976; Robbins 1993]. Only the earthworms and juvenile cricketscontained these suggested Ca:P ratios, with the remaining averaging a 1:4 Ca:P ratio.Excesses of dietary phosphorus and/or low dietary calcium levels can lead to condi-tions such as rickets, causing clinical signs such as lameness; weakened, deformed,or broken bones, or osteomalacia; and depressed reproduction [McDonald et al., 1973;Allen et al., 1993]. In addition, egg production and bone development in Cubantreefrogs (Osteopilus septentrionalis) and fox geckos (Hemidactylus garnoti) requirelevels of calcium that cannot be provided by certain insects alone [Allen et al., 1993].A number of ways to overcome calcium deficiency have been suggested. A highcalcium diet fed to insects can increase their calcium content; feeding alfalfa or com-mercially balanced diets to mealworms rather than bran or cereal grain substratescan greatly improve their nutritional quality [Martin et al., 1976; Frye, 1991]. Thediets of insectivores can be supplemented with noninsect sources of calcium [Studierand Sevick, 1992] or with calcium added to the drinking water [Martin et al., 1976].

All the species sampled in our study contained Mg levels adequate for thedietary needs of domestic birds and mammals (0.03–0.15% DM) [Robbins, 1993].Previous studies also determined that insects should easily meet the assumed magne-sium requirements of insectivores [Levy and Cromroy, 1973; Frye and Calvert, 1989;Studier et al., 1991; Keeler and Studier, 1992; Studier and Sevick, 1992], althoughno requirement studies have been conducted specifically with insectivores.

Trace element requirements of mammals (Cu, 1.6–6.0 mg/kg; Fe, 25–180 mg/kg; Mn, 3.7–50.0 mg/kg; Zn, 9.2–30.0 mg/kg) [Robbins, 1993] were met by most ofthe insects sampled; Mn concentrations were lower in supermealworms and waxwormsthan estimated dietary requirements based on domestic animal models. Earlier re-ported Cu values [Levy and Cromroy, 1973] and Fe values [Jones et al., 1972; Levyand Cromroy, 1973; Studier et al., 1991; Keeler and Studier, 1992; Studier and Sevick,

132 Barker et al.

1992] for insects have met these requirements, with the exception of the eastern tentmoth adult (<0.01 ppt) [Studier et al., 1991] and the larvae of the lettered sphinxmoth (Deidamia inscriptum) (15 mg/kg) [Levy and Cromroy, 1973]. Both sources ofearthworms appear to meet known mineral requirements for birds and mammals,assuming adequate bioavailability. Earthworms have been shown to accumulate met-als including Ca, Cu, Mn, and Zn from soils with high concentrations of these ele-ments [Ireland, 1979].

Differences in mineral composition of insects have been attributed to age, sea-son of collection, size, and/or gender [Studier and Sevick, 1992]. In nature, insecti-vores may obtain their required nutrient levels by diversifying selection or ingestingsoil with insects [Allen et al., 1993]. Detailed nutrient composition of whole inverte-brate prey may provide useful information in developing appropriate diets for thecare and feeding of insectivores and should be undertaken with these goals in mind.

CONCLUSIONS

1. Regarding proximate body composition of invertebrates investigated, larvalstages contained significantly more fat than adults. Crickets, which do not have alarval form, had higher fat as adults than nymphs (instars).

2. Insects and other invertebrates in general contain high levels of protein, al-though a portion may be chemically bound within the exoskeleton. Chitin (measuredas NDF) comprised ~15% of DM in most species.

3. Most invertebrates sampled met the dietary vitamin E recommendations fordomestic mammalian carnivores (20–80 IU/kg DM), with the exception of MightyMealysTM mealworms.

4. Insects are a poor dietary source of preformed vitamin A.5. Insects (with the possible exception of pinhead crickets) are a poor dietary source

of calcium and possess inverse calcium:phosphorus ratios. Earthworms contained higher,and apparently balanced, concentrations of both calcium and phosphorus.

6. All invertebrates sampled contained adequate levels of Cu, Fe, Mg, and Znto meet dietary requirements, based on domestic animal recommendations; only Mnlevels may have been deficient.

ACKNOWLEDGMENTS

A grant from the Howard Hughes Medical Institute to the Department of Biol-ogy, Manhattan College, helped fund this project. We thank Dr. Tramontano for hissupport and guidance, and F. Palasciano, T. Palasciano, and C. D’Arco for their helpin the acquisition of wild-caught earthworms. Dr. W. Graffam and six anonymousreviewers provided helpful comments on this manuscript. This research is part of acooperative agreement between the Department of Biology, Manhattan College/Col-lege of Mt. St. Vincent, and the Wildlife Conservation Society.

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