Common Summer Tree Pests & How to Spot Them with Alt Arb Ltd Part 1

As the days get longer and the weather warms up, our trees are busy growing, blooming, and bringing beauty to gardens and landscapes across Gloucestershire. But summer isn’t just a time of growth—it’s also peak season for a range of tree pests that can silently cause serious damage if left unchecked.

From aphids to caterpillars and tree borers, these tiny intruders can weaken even the healthiest trees, leaving them more vulnerable to disease and storm damage. In this post, we’ll walk you through the most common summer tree pests, how to spot the early warning signs, and what to do if you notice trouble brewing.

1. Aphids

What to Look For:

Aphids are small, soft-bodied insects that gather in large groups on new shoots, stems, and the undersides of leaves. They can be green, black, brown, or even pink depending on the species.

You may also notice a sticky residue called honeydew, which aphids secrete as they feed. This sugary substance often attracts ants and can encourage the growth of sooty mould, a black fungus that coats leaves and blocks sunlight.

Signs of Damage:

• Curling or misshapen leaves

• Yellowing foliage

• Stunted growth

• Presence of ants climbing the tree

• Black, sooty fungal patches

2. Caterpillars

What to Look For:

While some caterpillars are harmless or even beneficial, others can be highly destructive to trees. Keep an eye out for chewed or skeletonise leaves and fine silk webbing around branches, which is a tell-tale sign of infestations like the oak processionary moth or winter moth.

Note: Some caterpillar species, like the oak processionary moth, can cause allergic reactions in humans and animals—so approach with caution and never handle them directly.

Signs of Damage:

• Ragged or missing leaves

• Full defoliation of sections of the tree

• Weakening of smaller branches

• Silky webbing or tents in the canopy

3. Tree Borers

What to Look For:

Tree borers are beetles or larvae that tunnel into the wood of trees, damaging them from the inside out. You may notice small round holes in the bark, trails of frass (a sawdust-like substance), or bark that looks cracked or weakened.

These pests are particularly dangerous because they can affect a tree’s vascular system—cutting off its ability to transport water and nutrients.

Signs of Damage:

• Wilted or yellowing leaves

• Dead or dying branches

• Visible holes in the trunk or branches

• Loose, flaking bark

• Increased woodpecker activity (they feed on larvae under the bark)

Why Early Detection Matters

Left untreated, even a minor pest problem can escalate into a major threat to your trees. Pest-damaged trees are more susceptible to fungal infections, structural failure, and storm damage—and in worst-case scenarios, may need to be removed entirely.

The good news? Most infestations can be managed if spotted early. That's why regular tree inspections, especially during the growing season, are so important.

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So What’s Next?

This post is part one of our summer tree care series. In July, we’ll dive deeper into Poplar trees, which are particularly vulnerable to seasonal pests and diseases. We’ll explore the specific threats to look out for—and how to keep your Poplars healthy and thriving.

Need Help Identifying Tree Pests?

If something doesn’t look right, don’t guess—get in touch with Alt Arb. Our qualified tree surgeons offer professional inspections and practical solutions to keep your trees strong, safe, and pest-free all year round.

👉 Call us today or book an inspection online to stay one step ahead of summer’s tree pests.

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