Animals lacking a spine or any internal bone structures are classified as invertebrates. They possess an exoskeleton, or outer shell, which they shed as they grow. This process is called molting.
At some point in the past, people started keeping these strange and interesting animals as pets, and now a whole hobby has been built around keeping them. Unlike many traditional pets, they don’t need to be taken for walks, trained or given very large enclosures.
Below is a list of some commonly available invertebrates that can be great pets.
Hermit crabs are one of the most common first pets, but many aren’t given the proper care to survive very long.
In captivity, hermit crabs can live 10–20 years when given the right living conditions. They thrive in high humidity, along with a varied diet and buddies.
These crabs are surprisingly social and do very well in groups. Watching their interactions is one of the joys of keeping them.
A 20-gallon aquarium will provide decent room to roam. If adding more members to the group, a 55- to 75-gallon aquarium will work much better.
Hermit crabs need access to both fresh and saltwater. The salt used must be the kind made for marine fish.
Stick to natural shells, preferably the same size or a little larger than what the crabs are currently wearing. Avoid painted or decorative shells — they’re known to cause illness in the crabs.
To create a deep, moist substrate, use silica-based sand and coco husk. This substrate also provides a place for them to burrow into it from time to time and molt underground.
Humidity and Temperature
Keep the humidity level at 75–85% at all times. Comfortable temperature ranges are between 75–85 degrees Fahrenheit.
Lighting and Heating
If your house is on the cool side, you can add an under-tank heater to one side of the tank to add warmth for the inhabitants. A fluorescent tube light should suffice for viewing, and provide a day and night cycle for the crabs.
Avoid commercial foods — hermit crabs are very sensitive to preservatives and other additives.
A diet of varied veggies, fruits, leaves, flowers, crushed coral and calcium will benefit all crabs. They love meaty foods including dried insects, cooked meat, egg and more.
Some crabs enjoy handling, while others do not. Try to keep your hand flat and allow them to crawl on you to avoid any pinching.
Some crabs will actively climb your hands and clothes, and appear to like exploring a bit. Just keep handling out of the tank to a limit of 10–15 minutes — the humidity outside the tank isn’t really comfortable for them.
For more detailed information on caring for hermit crabs, visit this great care sheet.
Giant millipedes are multi-legged arthropods that are relatively friendly. There are multiple species available of varying sizes, and some can live 7–10 years.
Some of them sport lovely color schemes. Their docile nature makes them a great choice as a more easily handled invertebrate, and they don’t move too fast either.
If they feel threatened, they will curl into a tight spiral and secrete an irritating liquid from pores in their body. It can be harmful to your eyes or mouth, so wash your hands if this occurs. Some species may have a higher toxicity, so make sure to correctly identify what species you want.
Giant millipedes can be housed with their own kind and generally get along fine. They will even breed readily if both males and females are present. If you have breeding adults, make sure you can find the babies homes.
A 10- to 15-gallon tank will comfortably house a couple millipedes.
Millipedes like to burrow, so provide a 3- to 4-inch depth of substrate. A peat/soil mixture will work well. Sphagnum moss can be added on top.
Make sure there aren’t any pesticides in the soils you use. Keep the substrate damp, not wet, with regular misting.
Temperature and Humidity
A good temperature range is 75–85 degrees Fahrenheit, and a small dip at night should be fine. Maintain a high humidity around 75–80%.
Lighting and Heating
No special lighting is required. For heating, an under-tank heater can be used to add warmth to one side of the tank.
Keep a shallow dish of water for them in the tank. Clean it out and refill often.
Millipedes are herbivores that eat mostly decaying plant matter.
They can be fed vegetables cut into small pieces. Soft fruits and veggies work. If the food starts to decay, that’s alright — they prefer it that way.
Add some leaf litter for them, too. Just make sure it’s free of pesticides or other bugs.
Mexican Redknee Tarantula
These are one of the more hardy and docile tarantula species, and they tolerate some handling.
Reaching a leg span of about 5 inches, Mexican Redknees are colorful spiders. These are very long-lived tarantulas — a few have reached their 20s in captivity. Unlike tree-dwelling species, the Redknee is terrestrial and needs more floor space than height with respect to housing.
A terrestrial container or terrarium should adequately house 1 tarantula. Include a lid — these spiders can climb. A plastic terrarium-style critter-keeper will do just fine. Adding an overturned flower pot or driftwood will provide hiding spots.
Use horticultural vermiculite (not insulation type) or Eco Earth. Both hold humidity well and are made specifically for pets. It’s best to add a layer of at least 2 inches.
Temperature and Humidity
A steady 70–78 degrees F is a good range. A heating source may not be needed depending on your climate.
Humidity should be maintained at 50–60% in the tank. It is thought that raising the humidity during the molting process may help them.
Lighting and Heating
No lighting is needed, and heating isn’t necessary, unless you live in a cold climate.
Supply a small, shallow dish of water for the tank. Place a pebble or 2 to prevent drowning of prey items. Clean and refill often.
Offer properly sized crickets, superworms or roaches once a week. The size of prey and the frequency at which you feed will depend on the age and size of the tarantula.
Handling should be determined by how comfortable or stressed the tarantula is. Some keepers choose to forego handling to reduce the chance of stress to the animal.
Another potential reason for avoiding handling is the irritating hairs the tarantulas can flick off their abdomens when they feel threatened. These little hairs can irritate eyes, nose and skin. There is also the fact that they can bite.
However, some tarantulas do very well with a little handling, but care must be taken that they not be dropped — this can lead to injury or death. For such large spiders, tarantulas are still delicate.
Where to Find Them
Local and online vendors may carry the species you are looking for. Make sure they are reputable sources.
Connect with message boards relevant to what you’re interested in, and they may be able to point you in the direction of both breeders and vendors. You may also find some invertebrate pets needing to be rehomed by their keepers.
Watch these amazing hermit crabs in the wild:
Keeping Pet Invertebrates
Invertebrates can add a unique insight into their world when kept in captivity, whether kept as pets or in a collection.
Many of their instinctual behaviors remain unchanged, and keepers can observe several events during their life cycles that would otherwise be hidden. You learn each individual animal’s preferences and personality.
A novice keeper can gain knowledge and experience with beginner species and eventually graduate to keeping more difficult ones. The hobby can culminate in keeping and breeding species usually reserved for the more advanced keeper.
If conditions are right, some species can be bred. Some species of arachnid are quite sought after, and some pose a challenge to breed in captivity. It can be highly rewarding for experienced keepers to successfully breed these animals and provide more of them to the hobby.
Invertebrates may not be the typical cute and cuddly pet, but they are sure to intrigue and catch the eye of those willing to get up close to these unique animals.
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Angela DeRiso is a freelance writer passionate about the proper education, care and rescue of all animals we share our lives with. Her articles have been published on HealthyPets, Tampa Bay House Rabbit Rescue, The Suncoast Herpetological Society newsletter and more.