Mouthparts Hold Tight

Biological Strategy

Sheep tick

Eleanor Banwell

Image: Erik Karits / Pixabay / Free non-commercial use

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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Capture, Absorb, or Filter Liquids

The most common liquid used by living systems is water, which they require to survive. But there are many other liquids that provide nourishment, play a role in defense mechanisms, or serve other purposes. Water varies in its availability; it is sometimes plentiful and sometimes very scarce or only available as fog or mist. To minimize the energy required to capture, absorb, or filter liquids, living systems have strategies that take advantage of the unique properties of the given liquid. For example, water moves from a gaseous to liquid state when it encounters a surface colder than the air. Plants in forests that experience fog and clouds more than rain have strategies that condense liquid water from moist air.

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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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Mouthparts of tick hold tight using a combined ratchet and barb mechanism

Ticks are a familiar nuisance for anyone that enjoys hiking. Like all blood-feeding parasites, they can become considerably more than a nuisance when they carry and transmit infectious diseases such as Lyme disease. Unlike other biting insects, which bite quickly and leave before they can be discovered, ticks can hold onto their prey for days at a time, increasing dramatically in size during that time from their blood meal. To stay in place for such a long time, most ticks secrete a cement like substance from their mouthparts after biting, but one species, the sheep tick Ixodes ricinus doesn’t produce cement and it must hold on with physical force alone. This is more challenging than it might appear, as mouthparts specialized for insertion and feeding will be a different shape to those specialized for grip. Sheep ticks get around this problem with a combined ratchet and barb.

The mouthparts of sheep ticks include a two-part insertion needle with a jointed barbed tip. Insertion and attachment is a multi-step process where the tick first sweeps the skin with the tip to find a suitable point for insertion and then pushes through the skin’s surface. At first, the two halves of the insertion needle push in alternately, with the barbed hooks on the tip of one side forming the anchor against which the other pushes deeper into the tissue. Once in past a certain depth, the tick switches to a breast-stroke like movement, where the jointed tips first thrust in and then spread out, pulling the rest of the mouthpart in behind them. Once fully inserted, the barbs stay spread, anchoring the tick in place.

Here’s an animation showing sheep tick insertion in a host:

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