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the web of life in southern Africa

Thomisus (flower crab spiders)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Ecdysozoa > Panarthropoda > Tritocerebra > Arthropoda > Arachnomorpha > Cheliceriformes > Chelicerata > Euchelicerata > Arachnida > Araneae > Araneomorpha > Family: Thomisidae (crab spiders)

Thomisus sp. female with male waiting on her abdomen to mate. White Thomisus sp. with bee prey.
Thomisus sp.
Top: Thomisus female with male waiting on her abdomen to mate. Bottom: Thomisus sp. female. [image N. Larsen ] White Thomisus with bee prey. [image N. Larsen ]

The most conspicuous genus in the family. Spiders are short and squat, ranging in size from 3-11mm. The glabrous integument (exoskeleton) is cryptically coloured, taking on the colour of its surroundings. Thomisus is able to undergo white to yellow or pink colour changes depending on the flower they are sitting on. This colour change facilitates camouflage on flower ambush sites and is completed within 2 days. While colour patterns are species specific, colours can vary. Not all species have this colour changing ability as some species occur on bark or among grass seeds and thus are a cryptic brown. The first and second pairs of legs are noticeably longer and thicker than the last 2 pairs and are used for prey capture. The abdomen is triangular in shape, being widest posteriorly. The lateral eyes are situated on tubercles.

Thomisus is a sedentary spider and is usually noticed only when one sees a strangely positioned, usually upside down, insect and upon investigation, the insect can be seen to be in the grips of a spider. Thomisus waits for flying insects to settle, patient and motionless, with outstretched legs. She can detect them from 20mm and when within a range of 5-10mm, Thomisus closes her powerful front legs, catching the insect which can be up to 3 times her size. The insect is then bitten behind the head and killed. The insides are dissolved with enzymes and sucked from the exoskeleton and the empty, perfect form of the insect is dropped to the ground.

Often a small brown male can be seen riding piggyback on the female (see top left photo). The male seeks out a subadult female and waits for her final moult at which time she is incapable of resisting his advances or attacking him. He makes his move and mates and then leaves to seek another defenseless mate. The females probably secretes pheromones before the moult which attracts the males. After mating, she lays her eggs in a leaf curled much like an ice cream cone. She guards the eggs without eating and dies later leaving her offspring to disperse.

Text by Norman Larsen