Female Lord Howe Island stick insect. Photo Courtesy San Diego Zoo.
Female Lord Howe Island stick insect. Photo Courtesy San Diego Zoo.

Female Lord Howe Island stick insects have laid more than 500 eggs at the San Diego Zoo in the past couple of months, the first time the critically endangered species has done so at a North American facility, park officials said Thursday.

The Lord Howe Island stick insect breeding program at the zoo is part of an ongoing conservation effort to increase the numbers of the rare species — thought for decades to be extinct. The zoo is working with Australia’s Melbourne Zoo, which has been successfully breeding this species since 2003, when four individuals were brought into managed care after being rediscovered in the wild two years prior.

The San Diego Zoo has 40 adult females and 29 adult males in its breeding program. They hatched from eggs laid in Australia that were brought to San Diego in January.

Zoo officials said the insects are extremely difficult to rear, as the early life stages are delicate and require specific environmental parameters.

Lord Howe Island stick insect eggs — each about the size of a popcorn kernel — are kept in vermiculite, a soil additive that provides appropriate moisture for the eggs’ development. Every morning, staff checks for new eggs at the breeding facility.

The adults are divided into habitats that house between 13 and 17 individuals. Each habitat includes a hollow log, where the nocturnal bugs gather during the day, and a sandy container where the females can deposit their eggs.

The eggs and adults are maintained in an off-exhibit area where temperature and humidity levels can be tightly monitored and controlled.

When the insects hatch in spring 2017, the nymphs will be bright green, helping them to blend in with their host plant — Melaleuca howeana — a shrub native to Lord Howe Island. It has very small, green leaves and can grow up to 10 feet tall.

As each Lord Howe Island stick insect matures and molts, it will grow to be around 7 inches long and will gradually change from bright green to a shiny black-brown.

According to the zoo, plant-feeding insects like the Lord Howe Island stick insect are critical to their ecosystems because they are a link between the energy that green plants harness from the sun through photosynthesis. Amphibians, reptiles, birds and mammals that do not eat plants are dependent on insects as a food source, and their energy is transferred up the food chain as they are consumed, zoo officials said.

–City News Service