A captive breeding program for the critically endangered Lord Howe Island stick insect—or tree lobster—has been underway at the San Diego Zoo for just one month, and it is already hitting milestones. The Entomology department is caring for the first 73 nymphs that have hatched from 300 eggs the Zoo received on January 29, 2016. Entomologists are also preparing as the oldest nymphs complete their first instar, the growth period that occurs between molts. Molting is accomplished by shedding their exoskeleton—the protective covering around their bodies.
To shed its exoskeleton, the stick insect uses gravity. The nymph will hang upside-down from a host plant or the top of the screened enclosures where they’re kept at the San Diego Zoo. The body of the insect will expand and contract, causing the exoskeleton to separate along the top part of the thorax, the middle section of the stick insect’s body. Eventually, the insect will be able to pull its entire body out of the old exoskeleton; however, at this time the new exoskeleton is very soft and vulnerable and needs time to harden. The molting process itself takes less than an hour—and typically, the stick insect will eat the old exoskeleton, in order to recycle the nutrients it contains.
The stick insects grow approximately 6 to 10 mm during their first instar, and the Lord Howe Island stick insects are expected to go through five instars before reaching maturity in approximately seven months. The tree lobsters will continue to grow until their final molt; and after that time, they will have reached adult size and will never molt again.
The Lord Howe Island stick insect breeding program at the San Diego Zoo is part of an ongoing conservation effort to bring this rare species of stick insect—which was previously thought to be extinct—back from the brink of extinction. The Zoo received the eggs from Australia’s Melbourne Zoo, which has been successfully breeding this species since 2003, when four individuals were brought into managed care after the species was rediscovered in the wild in 2001. Eggs from this critically endangered insect were given to the San Diego Zoo to establish an assurance population, separate from the Melbourne group.