Scientific name: Acrostira euphorbiae
Family: Pamphagidae
Length: 67-71 mm (♀) and 30-31 mm (♂)
Distribution: La Palma, Canary Islands, Spain
Habitat: Scrubland of Euphorbia lamarckii, 40-680 m a.s.l.
Origin category: Endemic
Conservation status: Critically Endangered (CR)
The La Palma stick grasshopper (Acrostira euphorbiae) is a large, highly specialized grasshopper endemic to the small island of La Palma (Canary Islands, Spain). It is considered one of the rarest insects in the world with its only known native habitat restricted to the southwestern part of the island. This once plentiful insect became severely threatened by the loss of its habitat.
The habitat of this species consists of lithosols covered by xerophilous vegetation, namely E. lamarckii, located at an altitudinal range between 40-680 m. It selects preferably the areas of highest shrub density of E. lamarckii, and with soils lacking any high grass in which to bury their eggs. It is a monophagous species, exclusively feeding from the shrub on which it dwells, and is therefore also a bush-dwelling species, as opposed to most continental species that are mainly ground-dwelling. They are a macropterous species, with a low jumping capacity due to their poorly developed hind legs. Their camouflage, slow movements and elusive nature make them hard to find and observe. When approached, they will usually move around to the opposite side of the branch with as little movement as possible, keeping the trunk between them and their harasser, in the hopes of not being detected.
Their size ranges from 30 to 71 mm, and females are twice the length of the males. Due to their size and limited mobility, in this species it is the females that emit mating calls to attract males, by using the alar-notal mechanism in which the ventral edge of the metanotum and the basalar sclerite are rubbed together. This behaviour is found exclusively in females to announce their reproductive receptivity to the males, and females usually have to produce a series of anomalous sounds before they can emit a perfect mating call. The majority of nymphs hatch one or two months after the first rains in autumn, when the vegetation is the lushest and offers the the best feeding and camouflage opportunities for the new generation.
Its distribution is tiny, at around 20 km². The population size is likewise very small, about 200 mature individuals, all found in a single subpopulation, and is currently decreasing. From 2003 to 2008 the population decreased by 68%. There is a continuing decline in its distribution and extent and quality of its habitat; the only location of this species is strongly affected by illegal logging of its main food plant, wood harvesting, overgrazing by livestock, touristic recreation areas and wildfires. Besides these ongoing threats, its habitat is very likely to be destroyed by future landslides or volcanic eruptions. Therefore, the species is assessed as Critically Endangered (CR).