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Thomisus

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Thomisus
Thomisus onustus capturing a bee
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Infraorder: Araneomorphae
Family: Thomisidae
Genus: Thomisus
Walckenaer, 1805
Type species
Thomisus onustus
Walckenaer, 1805
Species

See text.

Diversity
145 species
male Thomisus kitamurai from Japan
female Thomisus kitamurai

Thomisus is a genus of crab spiders (family Thomisidae) with almost 150 species described. The genus includes species that vary widely in their ecology, but the best known crab spiders are those species that people call the flower crab spiders, because they are ambush predators that feed on insects visiting flowers. The flower crab spiders are the species for which the popular name was coined, because of their crab-like motion and their way of holding their front legs in an attitude reminiscent of a crab spreading its claws as a threat.

Description and habits

As with most Thomisidae species, Thomisus exhibit sexual size dimorphism: females are four to ten mm in length, whereas males are only two to seven mm. Many are brightly colored, usually matching the color of the flower in which they are waiting in ambush.[1] Not all species are flower-dwelling, but among those that are, at least some species can change their colour over a period of some days to match the flower colour.[2] Studies suggest that bees are inclined to avoid a flower that contains a spider-sized object of a non-matching colour; whether this is specifically a mechanism for avoiding crab spiders, or simply that they are not attracted to flowers whose nectar guides are obscured however, is a more difficult question.[3] The colour changes that such species can achieve are typically in ranges of white, pink, and yellow.

For example, in the Thomisus spectabilis species, the method of camouflage is similar to the Misumena vatia except the Thomisus spectabilis blend in with their environment while being visible to their prey, but not their predators. This species of crab spiders are UV reflective while the flower is UV absorbing creating a contrast between the spider and flower through the eyes of the pollinator.[4] The contrast created greatly attracts pollinators such as honeybees. This evolutionary method of camouflage increased the likelihood the crab spiders encountered prey, which in turn effects the fitness of the crab spiders. Due to the increased encounter rate of prey the spiders are able to focus energy on reproduction therefore leading to increased fitness in the spiders. The evolutionary method of camouflage greatly increases the survivability and fitness of crab spiders.

Distribution

female Thomisus okinawensis
South African species of Thomisus in ambush on Lavandula, by a flower too small for her to occupy
South African species of Thomisus disturbed on Lavandula inflorescence
female T. labefactus

The distribution of Thomisus species is almost worldwide, with the notable exception of most of South America.[5] Although Thomisus species can be found almost anywhere on earth, most species occur in the tropics and the warmer regions of the Old World, with fewer species in the region from New Guinea to Australia and the New World. Only T. guadahyrensis is known from South America, and only in Peru.

Species

As of February 2017, the World Spider Catalog accepted the following species:[5]

References

  1. ^ Murphy, Frances; Murphy, John (2000). An Introduction to the Spiders of South-East Asia. City: Malaysian Nature Society. ISBN 983-9681-17-6. {{cite book}}: Unknown parameter |lastauthoramp= ignored (|name-list-style= suggested) (help)
  2. ^ Filmer, Martin (1997). Southern African Spiders. City: BHB International / Struik. ISBN 1-86825-188-8.
  3. ^ Reuven Dukas and Douglass H. Morse ; Crab spiders affect flower visitation by bees ; OIKOS 101: 157–163, 2003
  4. ^ Gawryszewski, F. M., A. L. Llandres, and M. E. Herberstein. "Relationship between colouration and body condition in a crab spider that lures pollinators." Journal of Experimental Biology 215, no. 7 (2012): 1128-1136.
  5. ^ a b "Gen. Thomisus Walckenaer, 1805", World Spider Catalog, Natural History Museum Bern, retrieved 2017-02-25
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