Saturday, 5 November 2016

The ice crawlers

I have recently been learning about the Grylloblattodea, one of the smallest and the most threatened insect orders on earth. These fascinating insects are given the fantastic colloquial names of ice or rock  crawlers, and are found in cold mountainous areas of the Western USA and Asia.

In looking into the species in more detail, I found an excellent blog by Piotr Naskrecki, which is highly recommended reading here.

Grylloblatta campodeiformis - Piotr Nascrecki
Grylloblattodea get their name from the combination of features similar to Orthopteran (Grylloid) insects - external sword shaped ovipositor in the female, tentorium 'skull' structure - and Blattodean (cockroach) insects - five-segmented tarsi, multiarticulate cerci, assymetric male genitalia. There are number of features that can be used to distinguish the Grylloblattodea:

  • long and slender antennae
  • reduced (or absent) compound eyes, with no ocelli (simple eyes) present
  • apterousness (being wingless)
  • metathoracic spine (unique in the hexapods)
  • eversible sac on first abdominal sternum
  • long and slender legs, adapted for walking
  • long, multiarticulate cerci (at the rear of the animal)
  • long, sword-shaped female ovipositor (almost as long as cerci)
  • assymetric male genitalia
  • simple, chewing, foreward-facing mouthparts
Typical habitat in Western USA - Piotr Naskrecki

These are hemimetablous insects, meaing that they have an incomplete metamorphosis and their life cycle is a quite simple one of egg to nymph to adult. They are long-lived, with a lifespan of around five years, though this is thought to range to up to ten years. As typical of long-lived insects, the nymphal stage takes two years to mature.

The Grylloblattodea are cryophilic, meaning that they are adpated to cold environments. Their optimal temperature range is just 1-4 degrees C, though they can tolerate between -8 and 10 degrees C (and species in Asia can apparently tolerate even higher temperatures of 9-15 degrees C).

They are found at high elevations on glaciers, where they are mainly nocturnal, or at lower elevations in caves with permanent ice. Given the extreme environments in which they are found, their diet is quite broad, they probably cannot be too choosy. Species can be omnivorous scavengers of dead insects as well as plants, fungi and detritus.

The order Grylloblattodea contains one family - the Grylloblattidae. This contains  around 26 species (probably more) in five genera.

  • Grylloblatta - 11 species found in the USA
  • Grylloblattella - 2 species, found in China
  • Grylloblattina - 1 species, found in Siberia
  • Namkungia - 1 species, found in Korea
  • Galloisiana - 12 species, found in Japan and China
Galloisiana nipponensis, a blind species from Japan - Piotr Naskrecki

The populations of species in Grylloblatta have been reaersched in the Western USA. They are found in the Cascade mountain range, streching from British Columbia to Oregon, and the Sierra Nevada in California. In these areas they have been found in high altitude ice caes (300m-1000m) and north-facing talus and glacial margins (1500-3000m). Migration is limited, and they certainly cannot move at lower elevations, mneaning that populations are isolated.

Because of their limited ability to move, narrow environmental niche and small distribution, the insects are very vulnerable. The impacts of habitat loss and global warming are seen as strong threats to many species. SPecies in the order are placed in the IUCN red list in the near threatened, vulnerable, endangered and critically threatened categories.

Whilst the Grylloblattodea have successfully occupied particular niches through becoming specialists, habitat changes ate global warming pose a significant threat. This is an example of how specilaist species can be more extinction-prone that generalists. 

No comments:

Post a Comment