Frigate Island giant tenebrionid beetle (Polposipus herculeanus)

Also known as: Frégate beetle, Frégate Island beetle, giant Frégate beetle, giant tenebrionid beetle, Seychelles Frégate beetle
KingdomAnimalia
PhylumArthropoda
ClassInsecta
OrderColeoptera
FamilyTenebrionidae
GenusPolposipus (1)
SizeLength: 25 – 30 mm (2)

Classified as Critically Endangered (CR) on the IUCN Red List (1).

This remarkable beetle is the largest tenebrionid beetle in the world, and also one of the most endangered, being found only on the small Seychelles island of Frégate (3). Dark brown in colour, this flightless beetle has long legs and a large, rounded abdomen covered with small, raised tubercles (2) (4). Defensive glands produce a chemical secreted from the rear of the beetle, which has a musky smell and stains the skin purple (4).

Confined to the small Seychelles island of Frégate (3).

This arboreal species lives on trees and decaying logs, usually hiding in crevices and under flaking bark during the day, and coming out to feed at night (4). Large trees with flaky bark, fissures, cracks and crevices are preferred for the refuges they provide to hide from predators (4), and the Frigate Island giant tenebrionid beetle is particularly associated with the sangdragon tree (Pterocarpus indicus) (2).

This nocturnal beetle lives in large groups that often cluster tightly together in the cracks and crevices that form its daytime hiding places. Due to its large size and inability to fly, the Frigate Island giant tenebrionid beetle cannot travel very far, so normally remains around a small area. The furthest an individual has been recorded to travel is 19 metres, although many appear to stay on a single tree (4).

The life span in the wild is unknown, but two individuals collected as adults of unknown age survived over seven years in captivity. However, the average life span in captivity is only about half this (4).

Since the relatively recent human colonisation of Frégate Island, habitat destruction has been extensive. However, the beetles remained abundant on the island and also survived the invasion by introduced predators (brown rats) (5). A fungal disease affecting the sangdragon trees, on which this beetle relies, may represent a threat to the species (3) (5). Indeed, being restricted to just a single small island leaves the Frigate Island giant tenebrionid beetle particularly vulnerable to the effects of introduced alien species or disease, as well as to natural disasters or extreme environmental events, such as typhoons (5) (6).

In 2001, a successful rat eradication programme on Frégate was undertaken, removing this potential predator and threat (2), and population assessments were carried out in 1999 and 2001 (5). A breeding and research programme was also established at the Zoological Society of London’s Invertebrate Conservation Unit in 1996, with the hope that the information gained would better inform conservation management in the wild (3) (6). The initial captive population has now expanded to a full European Breeding Programme and involves institutions in the UK, Netherlands, Poland and Latvia (3). One potential conservation measure is the translocation of the beetle to other islands near Frégate, either from wild or captive stock (4). In addition, the DNA of this rare species has been entered and preserved in the ‘Frozen Ark’ (3).

For more information on the Frigate Island giant tenebrionid beetle see:

Authenticated (09/12/2006) by Justin Gerlach, Scientific Co-ordinator, The Nature Protection Trust of Seychelles.
http://islandbiodiversity.com

  1. IUCN Red List (June, 2008)
    http://www.iucnredlist.org
  2. Macdonald, C. (2004) Proceedings of the Sixth Annual Symposium on Zoo Research. The Federation of Zoological Gardens of Great Britain and Ireland, London. Available at:
    http://www.biaza.org.uk/resources/library/images/ARSP6.pdf
  3. The Frozen Ark: Saving the DNA of endangered species (October, 2006)
    http://www.frozenark.org/in.html
  4. Nature Seychelles (October, 2006)
    http://www.natureseychelles.org/index.php?option=com_content&task=blogcategory&id=28&Itemid=71
  5. Gerlach, J. (2006) Pers. comm.
  6. Zoological Society of London (October, 2006)
    http://www.zsl.org/field-conservation/island-ecosystems/