During the early days of the rainy season in Hong Kong, it is inevitable that many flying insects will intrude indoors. Among these bugs, flying ants, moths, stink bugs, termites or even beetles are frequently encountered, as they have a strong tendency to fly towards artificial light sources at night and enter the house by mistake. Sometimes you will find a less familiar guest, for example, a dragonfly-like creature clinging to the wall near the light source. This creature is probably a member of the Ascalaphidae family (Neuroptera), commonly known as the owlflies.
Owlflies, with over 450 described species, are a group of insects that belong to the order Neuroptera. They are distantly related to the dragonflies (Odonata), but are more closely related to alderflies (Megaloptera) and snakeflies (Raphidioptera), two smaller orders of insects. The owlflies possess a pair of large, bulging compound eyes, a relatively slender abdomen and two pairs of transparent wings. Unlike other members of the order Neuroptera (e.g. lacewings) that fold their wings along the abdomen at rest, some owlflies maintain their wings extended outward, resembling dragonflies. 𝘈𝘴𝘤𝘢𝘭𝘰𝘩𝘺𝘣𝘳𝘪𝘴 𝘴𝘶𝘣𝘫𝘢𝘤𝘦𝘯𝘴 (Walker, 1853) is one of the species found in Hong Kong, they also possess a slender abdomen and you can commonly observe them holding their wings out from the body at rest. They feature a broad yellow stripe running from the thorax to the end of the abdomen, as well as white transverse spots on each abdominal segment. They also have a body length ranging from around 25-50 mm and a wing span of around 70 mm, which are comparable to smaller and medium-sized dragonfly species. This shared physical appearance is the main reason why they are frequently misidentified as dragonflies. However, there are noticeable differences if you take a closer look. Owlflies have a pair of knobbed antennae in front of their head, which is very similar to the antennae of most butterflies. On the other hand, dragonflies have short, bristle-like antennae.
Similar to dragonflies, owlflies have carnivorous feeding habits. They are active aerial predators and can catch other insects. During the adult stage, certain species of owlflies can be observed hovering and darting at high speeds, chasing small flying insects in the air. They have a diverse diet, eating not only insects that can fly, like flies, beetles, lepidopterans (butterflies or moths), but also insects that seldom fly, like cockroaches, aphids, thrips and so on. The diversity of prey suggests that they feed not only during flight, but also while resting on plants. During the larval stage, owlflies are very different to dragonflies as they are terrestrial ambush predators, contrary to dragonfly larvae found in aquatic environments. The larvae of 𝘈. 𝘴𝘶𝘣𝘫𝘢𝘤𝘦𝘯𝘴 look similar to antlion larvae and have a pair of large, sickle-like jaws with sharp projections. In Hong Kong, they can be observed utilizing their enormous jaws to capture other small insects like ants above plants in autumn.
Most owlflies are nocturnal or crepuscular insects, meaning they are either active during the nighttime or active during dawn and dusk. In the case of crepuscular species like 𝘈. 𝘴𝘶𝘣𝘫𝘢𝘤𝘦𝘯𝘴 in Hong Kong, they can be attracted by artificial light sources at night, which is why we may occasionally find them indoors. However, there are some exceptions, like the European species 𝘓𝘪𝘣𝘦𝘭𝘭𝘰𝘪𝘥𝘦𝘴 𝘮𝘢𝘤𝘢𝘳𝘰𝘯𝘪𝘶𝘴 (Scopoli, 1763), diurnal and active during the daytime. The diurnal species usually have a pair of large compound eyes which give them excellent vision. Interestingly, the dorso-frontal part of the eyes is sensitive to the ultraviolet (UV) only. This specialization allows them to simplify their visual environment, making it easier to detect their prey. In UV vision, the contrast between the clear sky and the clouds is very limited, enabling them to easily detect their prey as contrasting dark spots against the sky. Thus, this unique eye structure improves the spatial resolution of the diurnal species, enhancing their success in catching prey.
If you are interested in learning more about owlflies, be sure to come to the Hong Kong Biodiversity Museum and delve deeper into the world of these chimera-like creatures. Besides, we are now having a Hong Kong Dragonfly & Damselfly Photography Contest - have a look at it. Make sure you do not submit these imposters to the competition! And if you enjoy this post, please share it with friends and follow us for more amazing biodiversity stories weekly.
Text: Tony
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