Small but powerful: the oribatid mite Archegozetes longisetosus Aoki (Acari, Oribatida) produces disproportionately high forces.

We investigated the holding and pulling forces generated by claws of the microarthropod Archegozetes longisetosus (Chelicerata, Acari, Oribatida) on three substrates with different roughness (R(a)=0.05 microm, 1 microm, 30 microm). Holding forces were measured perpendicular to the substrate using a strain gage force transducer; pulling forces were measured parallel to the substrate using an analytical scale. We found a significant positive correlation of surface roughness and the forces generated. Mites produced holding forces on horizontal rough surfaces (R(a)=30 microm) of up to 1180 times their weight; on vertical rough surfaces (R(a)=30 microm) they can pull with 530 times their weight, effectively involving only two pairs of legs. The relative forces are five times higher than theoretically expected for organisms of this size (<1 mm, 100 microg) and higher than any relative forces reported for insect claws. Muscles involved in claw action produced stresses up to 1170 kN m(-2), a value that is only excelled by decapod crustacean claw closer muscles. Ours is the first study of performance by chelicerate apoteles and claws and also the first to measure forces generated by any microarthropod.