Woolly Alder Aphids

Welcome back to Ask a Naturalist, your own personal Google for information on all things natural on PEI. Today we have an insect that people often mistake for a fungus. Meet Woolly Alder Aphids (Prociphilus tessellatus).

From a distance, Woolly Aphids do look like some sort of fluffy, fungal mould on the branch of a tree. But take a closer look and you’ll see that those fuzzy clusters are actually dozens – sometimes hundreds – of individual insects crowded together.

The bits of ‘wool’ are strands of wax that help protect the aphids from predators, weather, and their own excretions. Woolly Alder Aphids make a living by feeding on plant sap, which is high in carbohydrates but low in nitrogen (an important building-block of proteins). To get enough nitrogen, the aphids take in a lot of sap, filter out the nutrients they need, and excrete the excess as a sweet, sticky substance called ‘honeydew’. The aphids’ waxy strands help keep them from getting stuck in their own honeydew.

Not much goes to waste in nature, and that carbohydrate-rich honeydew attracts a range of Ants, Bees, Flies, and Lady Beetles; I’ve even seen Red Squirrels lapping it up. Ants are perhaps the most industrious when it comes to honeydew: they’ve been found to ‘farm’ aphids, protecting them from predators in exchange for their sweet poop.

Wondering if you can eat honeydew, too? Technically, yes, but remember it IS waste material, and it can also be colonized by harmful bacteria and fungi. I’d put it in the ‘not recommended’ category unless you know it’s fresh from the aphid. Grossed out by the thought? Honeybees sometimes collect aphid honeydew, so you may have already had some.

Despite their juice-sucking lifestyle, Woolly Alder Aphids don’t do any serious harm to the plants (though Woolly Apple Aphids can be a problem for fruit growers). Woolly Alder Aphids can be a bit of a nuisance if there’s a lot of them in a residential setting: their honeydew attracts wasps and it can drip onto things below, creating a sticky mess and encouraging an unsightly sooty mould to grow.  

 On the plus side, Woolly Alder Aphids support pollinators and other beneficial insects such as Lady Beetles and Lacewings that prey on them as well as on pests of agricultural and garden crops. (On the right side of the photo, you’ll see a Lady Beetle eating the aphids, although that one is the non-native Asian Lady Beetle [Harmonia axyridis]; this predatory habit is why it was brought to North America in the early 20^th century). On the whole, native Woolly Alder Aphids are more helpful than harmful to the Island ecosystem.

If you have a question about PEI’s wild side, it’s likely others do too! So, follow me here on Facebook and Instagram, join the conversation, and Ask a Naturalist about PEI untamed!