Scientists recently studied a rare butterfly called the northern oak hairstreak, Satyrium favonius ontario. They discovered that the species may rely on food sources other than nectar. The researchers also found evidence that the butterfly isn’t quite as rare as once thought. Their findings are detailed in the journal Annals of the Entomological Society of America.
The northern oak hairstreak is a small butterfly with muted brown coloration and a few orange markings. The butterfly has always been considered rare; only 3 were found in a previous 5 year butterfly census. The species had never been fully studied and very little literature was available on northern oak hairstreak biology. The butterfly is listed as Special Concern in the Massachusetts Endangered Species Act, granting the species some protections.
The research team spent two years studying the butterflies throughout the northeastern United States. They focused their efforts in the oak canopies of forests. The butterflies had generally been found on oak trees in the past and their larvae host in the trees. Their search paid off and the researchers found a total of 362 adults. Most of the sightings occurred during the summer, specifically mid-June to mid-July. Oddly, the researchers discovered that the hairstreaks weren’t actively consuming nectar. Instead, adults were spotted feeding on honeydew, produced by aphids, and oak galls, produced by cynipid wasps. They were also spending most of their time high up in the trees, where their tannish coloring helped them blend in. The researchers speculate that the butterflies may not be quite as rare as past research had suggested. Instead, the team believes that scientists and butterfly watchers hadn’t been looking in the right spots. Since the species doesn’t feed on nectar, they’re unlikely to be feeding on flowers close to the ground. Instead, they’re found in tree canopies, where their camouflage makes them difficult to find.
These findings show that northern oak hairstreaks rely on different food sources than other butterfly species. They feed on secretions made by wasps and aphids. This lifestyle allows them to stay safe in the canopies of oak trees, where they may be hard to spot. The researchers don’t necessarily recommend that the species have protections removed but they provide evidence showing that the hairstreaks aren’t as rare as previously believed.
Benedict L. Gagliardi et al. ‘Northern’ Oak Hairstreak (Satyrium favonius ontario) (Lepidoptera: Lycaenidae): Status Survey in Massachusetts, False Rarity, and Its Use of Non-nectar Sugar Resources. Annals of the Entomological Society of America (2016).