Velvet mite. Coloured scanning electron micrograph (SEM) of the head of a velvet mite (Trombidium holosericeum). This bright red arachnid is one of the largest mites found in northern temperate zones, with a body length of about 4mm. Its body is covered with fine hairs, giving it a velvety appearance. The bright red colour warns predators that it its toxic. Magnification: x50, when printed 10cm wide.