Saturday, February 26, 2011

Caring invertebrates

An Oxyopid spider that stayed put for 3 months
L. Shyamal - Creative commons / Wikimedia
We are not brought up on the notion of  invertebrates being caring and that presumably allows us to swat them without pangs of conscience. This spider sat on leaf of a Michelia tree in my garden, without making a movement for nearly three months. The kind of parental care given by invertebrates can be rather subtle. Invertebrates may carry their brood with them, stay over and conceal them, guard them actively, feed larvae or even sacrifice themselves as food for their brood. And it not just females, in some cases the males are involved in care of the brood. From my regular visits to the leaf while watering the plants, I imagine that this mother spider guarding her egg clutch never fed for all of three months unless she hunted by night (but these spiders are said to be diurnal) or found prey that came within reach.

Male water bug carrying eggs
Marshal Hedin - Creative Commons/Wikimedia
The Scientific American article (full text link below) by Douglas Tallamy includes a number of interesting pictures including a praying mantis that positions itself on the lower branch of a plant to intercept any predators that might climb up toward its young on the distal branches past it. 

Lethocerus indicus
Carrion beetles (including the male) regurgitate a fluid to feed their young. Water bugs in the genus Abedus and Belostoma have a peculiar system in which the female lays eggs on the back of the male which he carries until the eggs hatch.  Females  mate with multiple males and encumbered males never mate again until the eggs in their care hatch. The larger water bugs in the genus Lethocerus have the females laying eggs above the water on plant stems, and the male periodically climbs up to moisten the eggs, preventing dessication, and guarding the eggs by night. 

Great eggfly females stand guard near eggs
The social insects (mainly Isoptera, Hymenoptera) are of course well-known for the care of their brood however earwigs, carrion beetles, several bugs, cockroaches, butterflies and a host of others are known to show a range of parental care behaviours.  This extends even into the lower "insects" - the Diplura are known to show parental care in the form of guarding the eggs. Marine amphipods are also known for brood care. Freshwater leeches in the family Glossiphoniidae brood their eggs as do octopuses and other cephalopods. 

In general the idea is that parental care is more likely when the brood is smaller and "more precious" and when the organism is larger and long-lived.

Further reading

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