Ryan S. De Voe, DVM, MSpVM, DACZM, DABVP (Avian), Senior Veterinarian
This lecture will focus primarily on terrestrial arthropods such as arachnids, myriapods and insects. There is a significant amount of literature available to bring the veterinary clinician up to speed regarding captive management of various invertebrate species.1,7,9,11 One of the best books the author has run across is "Breeding food animals: live food for vivarium animals".6 This book covers captive maintenance and reproduction of most species of invertebrates found in captivity. Even so, nothing can top hands-on experience. Therefore the author recommends the interested clinician commit to personally keeping (at least) one of the more common "pet" species.
Many different options are available for housing captive terrestrial invertebrates ranging from simple pill vials with substrate to elaborate terrariums. As with all captive exotic animals the habitat needs to reflect the animal's natural history in order for it to thrive. Because most invertebrates are not overly destructive, they can be easily maintained in sophisticated terraria. The enclosure does need to be easily maintained as many species will quickly succumb to unclean conditions (especially when contaminated with fungus).
The author uses various sized pill vials with holes drilled into the top to house small invertebrate. The plastic aquaria with tight-fitting ventilated lids are ideal for larger animals. In reality, any ventilated enclosure with a tight-fitting lid could be used to house invertebrates. One needs to make sure the material the enclosure is made from is not toxic. Food grade plastics are generally safe, but other plastics can leach toxic chemical into the substrate, especially in a humid environment. With some species such as large tarantulas, millipedes and beetles, the cages need to be very secure as the animals can be strong enough to push lids open or chew through screening or plastic.
Many different substrates are appropriate for captive invertebrates. The selected substrate should allow the animal to behave as normally as possible and still be hygienic. The chosen substrate should not contain pesticides (obviously!), herbicides, fertilizer or other chemical additives. Perlite and other comparable additives should be avoided as well. Organic cactus potting soil and ground coconut shells are favorites of the author as substrates for most invertebrates. Some species, namely centipedes, enjoy a substrate of wet, rotting leaves and other plant material and will feed off it as well.
Provision of a hide area is paramount and the configuration should reflect the natural history of the animal. Some species can be provided with adequate hiding places by placing leaf litter or similar material on top of the substrate. Otherwise, flower pots, plastic containers with holes cut in the side, or commercially produced hide boxes are suggested. Many burrowing species will construct a burrow if given deep enough substrate. This can be frustrating as the animal will rarely be seen. These species will often use an artificial burrow that allows better visualization. Some species of tarantulas are noted for being very "webby" and provide their own hiding areas by casting webbing all over the inside of their enclosure. This is not very attractive or conducive for observing the animal, but if you pull the web structure down they will immediately rebuild it.
Because some invertebrate species are relatively soft-bodied and fragile it is important to choose appropriate terrarium furnishings. Plants and other objects with sharp spines or edges should be avoided. With terrestrial species there should not be furnishings that allow the animal to climb, as it may be injured if it falls.
The most challenging invertebrates to house are those that require high levels of humidity. It is difficult to balance this need for high humidity with adequate ventilation and sanitation. In ideal situations a humidity gradient should be established in the enclosure as it allows the animal exposure to high moisture levels, but allows other areas to dry out. Gradients are easiest to establish with burrowing animals. When provided with a deep enough substrate the lower layers of can be kept moist and the superficial layers can be relatively dry. The animals will burrow and come in contact with the lower, moist layers thus fulfilling the requirement for high humidity.
Most invertebrates do not enjoy bright light and will typically try to avoid it, so any illumination provided is for the benefit of the person viewing the animal. Subdued lighting is suggested if one feels some illumination of the enclosure is desirable. Exposure to natural sunlight or "full-spectrum" lighting is not necessary for invertebrates.
Proper water quality, presentation and availability are paramount in maintenance of captive invertebrates. Water requirements vary according to species with desert adapted species capable of efficiently conserving water, while those from rain forests or semi-aquatic environments will dehydrate quickly if not provided with enough water in the proper fashion. Some species can obtain all of the water they need from a proper diet. Most species will drink when water is available so every effort should be made to provide appropriate access.
It is safest to use water that would be appropriate for fish for maintenance of terrestrial invertebrates. Tap water can be used, but should be treated to remove chlorine or chloramines. Offering chlorinated water is thought to be associated with shortened life spans or ill-thrift syndromes by some keepers.
Many species will drink from a standing water source; however the risk of drowning is always a concern. To avoid drowning, many sources recommend providing water via a small sponge. This is inappropriate as sponges are impossible to keep clean and there is the possibility of toxins being present in commercially available sponges. A more effective solution is to provide water in a shallow water dish with stones or gravel in the bottom. This type of set up can easily be cleaned allows the animal to escape drowning if it falls in.
Many species will drink water drops following misting of the enclosure. Invertebrate species do not appreciate being directly misted, so the mist stream should be aimed at the enclosure's furniture, walls and substrate.
Anionic polyacrylamide (PAM) gel can be used for providing water to their invertebrates. It is sold at pet stores either in gel cubes or as crystals that can be rehydrated by the keeper. Some PAM products have added nutrients in order to improve the value of the invertebrate as a food animal. Another similar product is "cricket drink pillows". These items are composed of a durable polymer which will hold water when hydrated. The invertebrates suck water from the pillows and they can be re-hydrated when dry. The author has not used these products and suspects they present the same problem as sponges do with hygiene.
Maintenance of appropriate environmental humidity is important for captive invertebrates. Some species are incapable of consuming enough water to keep up with losses if the environment is too dry. A good example of this are the myriapods (centipedes and millipedes), which need very humid conditions to thrive. The myriapods produce wet droppings and lose relatively large amounts of water via evaporation through the respiratory system since there is variable, but generally less, ability to constrict the spiracles. Maintaining high environmental humidity almost always creates issues with hygiene, as the warm and wet conditions promote the growth of bacteria and fungi. Therefore, those species requiring high humidity are much more labor intensive to keep than some of the desert adapted species, as the keeper has to be vigilant with housekeeping.
Luckily most of the invertebrate species commonly seen in captivity are quite easy to feed. There is a wealth of literature available regarding diets for production species such as silkworms. A fairly large amount of literature exists regarding how to feed invertebrates to improve their nutritional value to animals that eat them.2,3,4,5 Many times these diets are not appropriate for long-term health of the invertebrate.
In this author's opinion the biggest concern regarding handling and examination of invertebrate species is the possibility of injury to the patient. Many of the commonly kept species are quite fragile and can be fatally injured with just a short fall. Terrestrial spiders and myriapods are some of the more fragile species. To compound the possibility of an injury, many invertebrates do not appreciate handling and will try to run or struggle to escape manual restraint. For these reasons it is recommended that the animal either be anesthetized (for a thorough exam), or restrained in a clear container (for a more cursory exam). Both methods allow for safe manipulation of the animal without an inordinate risk of injury.
It is impossible to describe a standard examination method for invertebrates as the anatomy can differ radically between species. Unfortunately there is no way to understand what is abnormal if you do not know what normal looks like. The interested clinician should go the extra mile to familiarize themselves at least with the commonly encountered species.
Close attention should be paid to all the invertebrate's bodily orifices. Discharges from the mouth or anus can indicate gastrointestinal disease. The respiratory openings are often the site of bacterial or fungal infections. In soft-bodied invertebrates the abdomen can be carefully/gently palpated and may reveal intestinal/colonic impactions. Hydration and/or status can be estimated by turgidity of the abdomen as well.
It is worth mentioning that some of the invertebrate species that may be encountered by veterinarians are dangerous to humans. Some spiders and centipedes have medically significant bites. Many of the tarantula species that are considered "harmless" have urticating hairs on their abdomens which they will shed when handled or stressed. These "hairs" can cause serious skin reaction and keratitis if one should end up in a person's eye. Some urticating hairs become airborne, which makes them more likely to end up in someone's eye or allow them to be breathed into the lungs where they cause variable reactions. Some tarantula keepers' respiratory tracts become sensitized to the hairs to the point where they cannot even be in the same room with a spider that possesses them. Even innocuous species such as centipedes can discharge irritating chemicals from their bodies. Protective gear such as gloves (minimally), eye protection and respiratory protection are recommended depending on the particular species being examined.
Anesthesia of terrestrial invertebrates should not provide too many difficulties to most clinicians. They can easily be anesthetized in chambers with isoflurane or sevoflurane (via a machine or soaked gauze). The author has found that a number of tarantula species tend to only reach light planes of anesthesia using isoflurane or sevoflurane. This short duration of immobilization sometimes necessitates either working with the animal in the anesthesia chamber8 or repeatedly moving it in and out of the anesthetic gas. Injectable anesthetics are not recommended due to their unpredictable and sometimes irreversible effects. No information exists regarding analgesia for terrestrial invertebrate species.
Monitoring terrestrial invertebrate anesthesia is dicey at best. Most do not actively respire, so there are no respiratory movements to monitor. Sometimes heart movements can be detected, but occasionally cardiac movements will cease for periods of time during the anesthetic episode with no ill effect on the patient. The best advice is if an animal does not recover immediately from anesthesia; do not immediately assume it is deceased. It should be placed in a thermoneutral, oxygenated environment and not considered dead until it shows obvious signs of rigor or decomposition.
Hemolymph collection is not a difficult procedure with most invertebrates that possess open circulatory systems. For instance, with tarantulas, the convention is to find the cardiac movement on the dorsal abdomen and try to draw the sample from the tubular heart. In reality, due to the open circulatory system, you could stick a needle almost anywhere into a tarantula's body and withdraw hemolymph (as long as you didn't skewer a parenchymatous organ!). Refer to the literature for descriptions of the recommended "hemo-puncture sites in various species.7,12
The real trick to hemolymph collection is knowing what to do with it after you have it! Invertebrate circulatory cells and biochemical parameters are not well-described, at least in the veterinary literature. At the very least, in the author's experience, it seems that circulating amoebocytes show changes similar to the toxic changes seen in neutrophils/heterophils when a tarantula is sick. Also, many ill invertebrates are septic, so occasionally circulating bacteria are detected via cytology. Hemolymph can also be submitted for culture.7,12
Since invertebrate medicine is in its relative infancy, all information is potentially important. Therefore, it is the author's habit to swab, scrape or aspirate every lesion or discharge and perform at least cytology. Although the host cells may be unidentifiable, one may recognize potential pathogens and therefore be able to make an educated decision about therapy. Cytologic exams of oral swabs from tarantulas and other chelicerates are recommended as the oral cavity is frequently parasitized in these species.10,12
1. Breene, R.G. 2000. Concise care guide for the 80 plus most common tarantulas. American Tarantula Society. Carlsbad, NM.
2. De Voe, R.S. 2009. Captive invertebrate nutrition. Vet Clin North America Exotic Anim. Pract. 12:349-360.
3. Finke, M.D. 2003. Gut loading to enhance the nutrient content of insects as food for reptiles: a mathematical approach. Z Biol. 22(2):147-162.
4. Finke, M.D., S.U. Dunham, and J.S. Cole. 2004. Evaluation of various calcium-fortified high moisture commercial products for improving the calcium content of crickets, Acheta domesticus. J. Herp. Med. Surg. 14(2):17-20.
5. Finke, M.D., S.U. Dunham, C.A. Kwabi. 2005. Evaluation of four dry commercial gut loading products for improving calcium content of crickets, Acheta domesticus. J Herp Med Surg. 15(1):7-12.
6. Friederich, U., and W. Volland. 2004. Breeding food animals: live food for vivarium animals. Krieger Publishing Co. Malabar, FL.
7. Lewbart, G.A. (ed.). 2006. Invertebrate Medicine. Blackwell Publ., Ames IA.
8. Melidone, R., and J. Mayer. 2005. How to build an invertebrate surgery chamber. Exotic DVM. 7(5):8-10.
9. Murphy, F. 1992. The care of spiders in captivity. In: Cooper, J.E., P. Pearce-Kelly, and D.L. Williams (eds.). Arachnida: proceedings of a symposium on spiders and their allies. The Zoological Society of London. London.
10. Pizzi, R., L. Carta, and S. George. 2003. Oral nematode infection of tarantulas. Vet Rec. 152:695.
11. Rubio, M. 2000. Scorpions: a complete pet owner's guide. Barron's Educational Series. Hauppauge, NY.
12. Williams, D.L. 1999. Sample taking in invertebrate veterinary medicine. Vet. Clin. North America Exotic Anim. Pract. 2(3):777-801.