Newsletter #180 August – The Rich Month of Summer

Newsletter about nature and science

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M.P.Gerkema

Aug 05, 2025

August – The Rich Month of Summer

August has traditionally been known as the harvest month. These days, much of the harvest is already in, thanks to extensive mechanization that—weather permitting—makes for a very swift process. The month is named after the first emperor of the Roman Empire, and he can consider himself honoured: August feels like the ultimate summer month. On average, it brings around 25 warm days (above 20°C), 8 true summer days (above 25°C), and in recent years, an increasing number of tropical days. The sun now shines about ten hours more than it used to, and rainfall has increased by roughly 25 mm—totalling 86 mm. Still, on average, August is slightly cooler than July. Due to shortening days, the sun shines 20 hours less than in July.

In the natural world, birds stand out in August mostly by moving on or flying away. For insects, however, August is peak season: many plants are still in bloom. Few new species begin flowering now, but among them are three troublesome exotic invaders from the Caucasus, the Americas, and Japan. Let’s talk about those.

The best-known is the giant hogweed—a towering member of the umbellifers, growing 2 to 3 metres tall with flower clusters up to 50 cm and leaves nearly a metre wide. Originally introduced from the Caucasus around 1900 as a garden plant, its spread exploded in the second half of the 20th century. The trouble lies in its sap, specifically the chemical furocoumarin, which—transmitted via stiff hairs on the leaves and stem—can cause severe burns when exposed to sunlight. Best to remove it before it flowers (see tips below), or let sheep and pigs devour it—they know what to do.

Then there’s common ragweed (Ambrosia artemisiifolia), a plant with highly allergenic pollen that can cause intense hay fever. It was first introduced around 1875 via hay from the US and is now mostly spread through contaminated birdseed. Thanks to climate change, it’s also slowly advancing northward. Standing 50–150 cm tall with deeply divided leaves (resembling mugwort), its drooping yellow flower clusters are the male parts releasing allergenic pollen. Besides gardens, it thrives on sandy farmland and wasteland.

The third invader may be the most stubborn: Japanese knotweed. Once a decorative import from Japan, it grows 1–3 metres tall, with large egg-shaped leaves, reddish stems, and small white to pinkish flowers. The real issue is its aggressive growth—just a tiny fragment of rhizome can regrow, crowd out other species, and even damage foundations and drainage systems. Complete excavation is the only solution. Pigs reportedly enjoy eating the roots, and there’s hope for a Japanese parasitic psyllid to help—if it doesn’t create new problems, of course.

Enough about the exotics. Another plant worth mentioning is ivy, which begins blooming now—not the showiest, perhaps, but incredibly important for insects in the months ahead. Thankfully, we can still enjoy our native hogweed and other umbellifers like Joe-Pye weed, spotted hemlock, valerian, and sweet William. They’re well worth a closer look—hoverflies, wasps, soldier beetles, and ladybugs are frequent visitors. Thistles still attract plenty of butterflies and insects too, as do evening primroses, purple loosestrife, and both hairy and common fireweed. Water lilies are still blooming, as is mallow. On the heathlands, common and cross-leaved heath are in bloom, accompanied by grasshoppers and digger wasps.

Bird-wise, August is a month of movement. Starlings and spoonbills gather in large flocks after the breeding season, while many of our nesting birds have already departed or are about to. Migrants from Scandinavia begin passing through, including ruff, greenshank, whimbrel, wood sandpiper, and green sandpiper. Brent geese, sanderlings, redwings, bramblings, and wigeons arrive to spend the winter. In short: autumn is already announcing itself.

🌿 Tips for August

Watch the bird migration! Use binoculars—or better yet, a telescope—on the North Sea coast, the Wadden Islands, or around the Veluwemeer.
Visiting heathlands? Keep an eye out for migrating raptors.
Make a checklist of which birds haven’t left yet, like lesser whitethroats, garden warblers, blackcaps, and common whitethroats—and note the true residents like the robin, wren, and our familiar tits.
Want to remove invasive plants? Prepare well (at the very least: gloves!), and try to dig out the entire plant, including roots and rhizomes. Avoid skin contact, especially with giant hogweed and ragweed.
Never dispose of invasive plant material in your green bin or compost heap—always put it with residual waste.

Menno en Erwin about Nature and Science

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