Dragonflies as a group:
Dragonflies (Anisoptera) and their relatives the damselflies (Zygoptera) form an order called the Odanata (there's another curious group called the anisozygoptera which we won't discuss here). Dragonflies can be distinguished from damselflies by their bulkier build, larger size, and style of flight. Both groups are obligate predators (meaning that is there sole source of nutrition) both as nymphs and as adults.
As young, dragonflies and damselflies are called nymphs (or sometimes larvae or naiads) and are fierce predators of the bottom of ponds and streams. The two nymphs are quite distinct, with damselflies featuring 3 fan-like gills out of their rear end, while dragonfly nymphs have opted to invert these gills inside their own anuses for reasons best known to themselves. The mechanism by which dragonfly nymphs circulate water via their gills means that they effectively breath through their anus, and can contract sharply to get water from their behind and shoot through the water, which they do in times of distress. Out of distressful times, they also use this mechanism to jettison faeces with enormous force, to the point that it can frequently leave the tank in our aquaria.
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After gaining the required body-mass and going through several skin-moults underwater, dragonflies and damselflies must undergo the dangerous transition into their adult form. This requires bursting through the exoskeleton on the back of their thorax and 'peeling' their body backwards. Wings begin shriveled and must be pumped full of hemolymph (insect blood) to inflate into useful structures. Dragonflies and damselflies imagos (final adult stage of development) are feeble fliers for the first day or so of life. Much of their exoskeleton will take time to dry. Over this drying and hardening period the emerged damselflies and dragonflies develop their deep and darkened colouration. New imagos can often be spotted by their pale, translucent pallor.
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A damselfly emerges from its nymphal skin (afterwards called an exuvium)
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A southern hawker (Aeshna cyanea) performs typical hovering and patrolling behaviours around a pond.
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While damselflies may catch aerial targets, they are also proficient gleaners (snatching prey from plants or the ground). While some dragonflies do glean (the oddball Gomphidae), the majority of species are focused around aerial predation.
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Broad-Bodied Chaser (Libellula depressa)
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The broad bodied chaser is a common species in the UK, with adults flying from late May through until mid July. Young adult males and females are yellow but males will take on a powder-blue appearance over time. Chasers and skimmers (the genus Libellula) are highly territorial and males invest a large amount of energy in chasing both rivals and potential mates. Unlike the hawkers (Aeshna), chasers will also spend time perched and sally from a perch to intercept prey.
We use broad-bodied chasers in the lab as they can be grown from captive nymphs and emerge within the lab. While chasers brought in from the wild will often refuse to behave in a captive setting, individuals grown within the lab are more readily persuadable. We also can then control the dragonfly's exposure to stimuli over time to better understand whether their hunting prowess is tuned over time via learning.
We use broad-bodied chasers in the lab as they can be grown from captive nymphs and emerge within the lab. While chasers brought in from the wild will often refuse to behave in a captive setting, individuals grown within the lab are more readily persuadable. We also can then control the dragonfly's exposure to stimuli over time to better understand whether their hunting prowess is tuned over time via learning.
Common Darter (Sympetrum striolatum)
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The common darters begin appearing towards the end of July and during are present in much of the UK late into the Autumn. While they are not necessarily the most noticeable dragonflies, they are likely the most numerable. The darters generally hunt from a perch (sallying) and are territorial but can be seen in high population densities (especially in warm sunny spots early in the morning).
The high abundance of the common darter makes them an extremely useful, if seasonal, addition to the lab. Many darters can be flown in the flight arena at one time, allowing for both conspecific interaction and predatory interactions to be observed in the same space. Darters are small (< 4 cm from nose to tail) but are able to carry tracking markers that will allow us to use motion capture to study their movement.
The high abundance of the common darter makes them an extremely useful, if seasonal, addition to the lab. Many darters can be flown in the flight arena at one time, allowing for both conspecific interaction and predatory interactions to be observed in the same space. Darters are small (< 4 cm from nose to tail) but are able to carry tracking markers that will allow us to use motion capture to study their movement.
