Quick as a crab
QZELDA BOSCH from Vanderbijlpark writes: My daughter Nerike (14) was picking lavender flowers in our garden when she found this pink spider that had just caught a bee, even though the spider was smaller than the bee. What kind of spider is it, and are those flies sitting on the bee?
AEntomologist DUNCAN MACFADYEN says: This is a flower crab spider. Its first two pairs of legs are characteristically longer and stronger than the last two. The spider’s name is derived from its crab-like motion and the way it holds its front legs – reminiscent of a crab spreading its claws when threatened. This species is often strikingly coloured. It can be white, yellow or shades of pink as Nerike discovered. Like a chameleon, a flower crab spider can change its colour over several days to blend with its surroundings. It’s an ambush hunter, sitting and waiting for its prey. Its venom acts quickly on insects, enabling the spider to catch prey significantly larger than itself. To eat its prey, the spider will use its fangs to pierce tiny holes in the body of its victim, then suck out the body fluids. The flies on the bee are called jackal flies (or freeloader flies) and they’re feeding on leaking juices. The term for this kind of scavenging insect is a kleptoparasite. There are many colour variants in the wild, the most common of which are caused by a shortage or an oversupply of melanin – the pigment responsible for dark colour in feathers. This pale groundscraper thrush has a shortage of melanin, known as partial albinism (sometimes called leucism). The normal-coloured feathers and the bird’s dark eye show that it’s not a complete albino. The number and position of white feathers in a bird with partial albinism vary considerably and are typically not symmetrical: Sometimes only one tail feather or flight feather is affected. Birds with extreme variations usually don’t have a long life expectancy. They are more vulnerable to predators and their feathers are weaker because melanin plays an important role in strengthening the feather structure. That’s the reason why a raptor’s flight feathers usually have black tips. The amount of white tends to increase with age.