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Insects and Other Arthropods as Food 629

While there are only limited data on the B-vitamin content of wild insects, there is a significant
amount of information for commercially-raised insects (Finke 2002, 2013, 2015a, 2015b). These
data suggest that, in general, insects are good sources of most B-vitamins. Some species such as
crickets are moderately low in thiamine, but a diet of mixed species of insects should provide
adequate amounts of all the B-vitamins.

Other­Nutrients
In addition to the known nutrients, insects contain a variety of other compounds that may be uti-
lized by insectivores. These include inositol, cholesterol, taurine, and other compounds (Cerda
et al. 2001; Ramsay and Houston 2003; Finke 2015b). While some of these compounds are required
by other species (i.e. taurine for cats and inositol for some species of fish), there currently are no
data to suggest they might be required by insectivores, including birds. Taurine, an amino sulfonic
acid, is of particular interest. It is found in a wide variety of animal tissues, including some species
of invertebrates. Crickets, grasshoppers, flies, moths, and spiders are rich sources of taurine, while
most species of insect larvae contain little if any taurine (Bodnaryk 1981; Massie et al. 1989; Finke
2002, 2013, 2015a; Ramsay and Houston 2003). Ramsay and Houston speculated that the prefer-
ence of blue tits (Parus caeruleus) for spiders during their nesting season may be due to their high
levels of taurine.

­ Feeding­Captive­Insectivorous­Nestlings

As the primary food for many wild nestlings, insects in general should supply adequate levels of
protein, amino acids, fatty acids, plus most minerals and vitamins. As noted in the previous sec-
tion, during the breeding season, adult wild birds of many species provide additional calcium to
their nestlings in the form of either calcium-rich invertebrates or calcium supplements to support
skeletal mineralization (Reynolds et al. 2004; Reynolds and Perrins 2010). Assuming an adequate
supply of foodstuffs, wild birds are presumably able to select a variety of arthropods that, in the
proper proportions, provides nestlings a diet that is sufficient for growth. Because nestlings in cap-
tivity are often fed only a few species of cultured insects (typically, crickets, mealworms, and wax-
worms), several nutrients are of special concern. Rehabilitators feeding insects to growing birds
should be primarily attentive to calcium, vitamin A, and, if adequate sunlight or full-spectrum
lighting is unavailable, vitamin D. The importance of additional nutrients such as omega-3 fatty
acids (and overall fatty acid profile) and taurine may be significant, although more work in this
area is warranted.

Insect-based­Diets

Cultured insects presumably offer a close approximation to the natural diet of insectivorous nest-
lings; however, they are expensive, and supplementing them with appropriate amounts of selected
nutrients can be challenging. Supplementation of insects is typically done in one of several ways.
The most common practice used in zoos is gut-loading, which involves feeding insects diets that
augment their nutrient profiles via food retained in their gastrointestinal tracts. The calcium con-
tent of waxworms, house crickets, mealworms, and silkworms can all be increased 5 to 20-fold by
feeding a high calcium diet (e.g. Strzelewicz et al. 1985; Klasing et al. 2000; Hunt et al. 2001; Finke
2003). Other nutrients such as vitamin A can also be added using this method (e.g. Finke 2003;