Hooks Aid Underwater Attachment

Biological Strategy

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Attach Permanently

A living system can conserve energy by attaching permanently to a particular site because it can take advantage of resources that come its way, rather than expending energy to move to resources. A permanent attachment, intended to last the lifetime of the living system, creates special challenges. For example, physical mechanisms, such as the anchor that holds a marine algae to the ocean’s bottom, must be able to withstand forces that can pull it off its substrate. Chemical mechanisms, such as a barnacle’s glue, must avoid both physical and chemical breakdown, such as being dissolved by water.

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Attach Temporarily

Living systems must sometimes, temporarily, stay in one place, climb or otherwise move around, or hold things together. This entails attaching temporarily with the ability to release, which minimizes energy and material use. Some living systems repeatedly attach, detach, and reattach for an extended time, such as over their lifetimes. Despite being temporary, these attachments must withstand physical and other forces until they have achieved their purpose. Therefore, living systems have adapted attachment mechanisms optimized for the amount of time or number of times they must be used. An example is the gecko, which climbs walls by attaching its toes for less than a second. Other examples include insects that attach their eggs to a leaf until they hatch, and insects whose wings temporarily attach during flight but separate after landing.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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The legs of blackfly larvae anchor them to silk pads attached to the substrate via numerous hooks.

“Blackfly larvae, even when very small, produce large amounts of silk which serves several purposes. First, silk is used for anchorage and explains the extraordinary capacity of blackfly larvae to remain attached or move in fast-flowing microhabitats. The larvae have numerous hooks, arranged in characteristic rows, encircling the tips of the anterior (thoracic) and abdominal prolegs (Fig. 5.5, p. 113). These help larvae to anchor firmly onto silk pads attached to the substrate. In species dwelling in particularly fast flow, the number of hooks on the abdominal proleg may exceed 8000, compared to only 500 in species living at slow velocity (Crosskey, 1990).” (Giller and Malmqvist 1998:116)

Last Updated August 18, 2016

References

Book

The Biology of Streams and Rivers (Biology of Habitats Series)

18/02/1999 | Paul S. Giller

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