Bug of the Year was created to celebrate the spectacular and often overlooked invertebrates of New Zealand. Backed by Te Papa, Collection Technician Invertebrates Shaun Thomson talks about one of this year’s nominees – a tiny fly with a jewel-like shimmer and a life cycle that borders on the unbelievable. Apsona, the sapphire spider fly, combines beauty with an unusual spider parasitising existence – exactly the kind of invertebrate that deserves your vote.
Since 2022, the annual Bug of the Year competition has celebrated the extraordinary diversity of New Zealand’s invertebrates, highlighting species that often go overlooked yet play vital roles in our ecosystems. The competition shines a light on creatures with unusual lives and strange adaptations, reminding us that some of our most fascinating wildlife is often the least well known. This year, one such nominee is Apsona, the sapphire spider fly.
Apsona are roughly the size of a honeybee and are coloured a spectacular metallic blue. Their eyes are holoptic, meaning they cover almost the entirety of the head. They have a proboscis, a modified mouthpart used to suck up nectar, that is almost as long as their body. Covering their bodies are long yellow hairs that are effective at picking up pollen and give them a fluffy appearance like that of a bee.
They are only found in New Zealand, where they occur in scattered locations throughout the North Island and the northern half of the South Island, where they are usually found in high-quality forest and subalpine habitats. Although they are fairly widespread, they are very rare throughout most of the country, but can be abundant in a few locations, such as Arthur’s Pass in the South Island. This patchy distribution makes Apsona both an elusive species and a fitting candidate for Bug of the Year, representing invertebrates that are widespread yet seldom noticed.
Spider parasites
Like all other small-headed flies, Apsona are parasites of spiders. Although nothing is known about their exact infection method, species of small-headed flies generally begin by laying their eggs in places where their hosts are common. The eggs then hatch, and larvae emerge, which inch along the ground searching for a host. After locating a host, the larvae inch closer and climb up the leg and onto the abdomen. Here, the spider is unable to easily kick them off, and the larvae are able to drill into the abdomen and enter the spider. Once inside, the larvae then make their way to the book lungs, the spiders’ respiratory organs, and settle inside. In the book lungs, the larvae slowly develop, a process that in some cases may take several years. Once they are ready to become adults, the larvae burst out of the abdomen and feed on the remains of the spider. They then finally pupate and turn into fully formed flies, ready to find food and produce offspring.
American cousins
Apsona are closely related to other metallic-coloured small-headed flies such as Eulonchus and Lasia in North and South America. Collectively, they form a group of flies termed the “Panopinae”.
So far, members of this group are recorded only parasitising primitive spiders such as tunnelweb and trapdoor spiders. Because of this, it is presumed that Apsona also parasitises more primitive spiders, possibly even targeting the endemic tunnelweb spider Porrhothele antipodiana, which is also a nominee for Bug of the Year. Confirming the identity of the spider host of Apsona remains an important area for future research.
Nectar feeders
Once they become adults, Apsona feeds on flowers, using their long proboscis as a straw to suck up nectar. The flies can hover above the flowers, allowing them to feed without needing to land. As they hover between flowers, their wings beat fast enough to create a shrill buzzing sound. When they choose to land on the flowers, large amounts of pollen get caught in the flies’ long hairs, causing them to become dusted in pollen. Because of this, it is possible that Apsona act as pollinators, although this still requires research to confirm.
Vote Apsona for Bug of the Year
With its beautiful metallic colour, strange spider-parasitising life cycle, and possible role as a pollinator, Apsona are one of New Zealand’s most remarkable flies. Found nowhere else in the world, they are a fitting representative of our unique invertebrate fauna. By voting for Apsona as Bug of the Year, you can help give this extraordinary species the attention it deserves.
