As any parent would attest, the love for a child is unfathomably deep and brings with it an irresistible desire to protect, guide and support, even if that should leave the parent without.
There are no limits to the sacrificial extent, and this is a pattern reflected across much of the natural world. In terms of an ultimate sacrifice, though, few animals can match that offered by a female lace-web spider.
There are three known species of lace-web spider in the British Isles. Also known as lace-weavers, they form part of the family Amaurobiidae and are similar in appearance although they differ slightly in size. The largest is the black lace-web (Amaurobius ferox), which is also the least well distributed, occurring across much of lowland England, Wales and Northern Ireland but scarce in Scotland.
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Found in damp or shaded corners in gardens or outbuildings, the adult female (the larger sex in all three species) has a body length typically between 10 and 15mm. As the name suggests, the black lace-web is the darkest in colour of the three species but still has the pale brown markings that are more prominent on similis and fenestralis.
Do lace-web spiders bite?
The abdomen of all three species is rounded, though not as bulbous as orb-weaver spiders, or the false widow species with which they are sometimes confused. They share similar habitats to false widows, which adds to potential misidentification, as does the fact that lace-webs can bite, although incidents are rare and the pain apparently mild.
Lace-web spiders are most active at night, spending daylight tucked into a silk tube on the edge of a flat, tangled web. The webs are often spun in tight areas, beneath window ledges or stones, or in dense vegetation, enabling the spider to remain discreet. In order to help snare prey, they spin silk through a tiny organ known as a cribellum, which agitates the thread to create a sticky, Velcro-like fibre. This gives the web a lace-like appearance after which the spiders are named, and the web is where an extraordinary act of parental sacrifice takes place.
The mother-eating spider
Having mated, the female spider creates a small sac from densely spun silk into which she lays her eggs. She then guards the sac for around a month as the eggs incubate, whereafter between 60 and 180 spiderlings emerge and remain with their mother. After a couple of days, the mother begins to cover the young with a fine silk layer which prompts them to move beneath her abdomen. There, they feed on fresh, but inviable, ‘trophic’ eggs, which are produced as a food source rather than for reproduction.
Following this, the spiderlings are able to grow sufficiently to achieve moult, and once that is complete the mother again agitates the silk to stimulate her offspring. On this occasion, they swarm across their mother’s body, biting her and injecting digestive enzymes into the abdomen that enable them to eat her.
The mother’s final act is to offer herself as a meal to her young in a behaviour known as matriphagy (literally 'mother-eating'). An act that is surely the ultimate parental sacrifice.
