Guide

Look closerInsects

Leaf packs in brooks and the insect larvae that eat them

November to December

After leaves fall, small streams collect them in soggy piles called leaf packs against rocks and sticks. Some aquatic insect larvae, including crane flies and certain stoneflies and caddisflies, chew on those leaves through fall and winter.

Why this time of year

By November leaf fall has filled woodland brooks, and after a few weeks underwater the leaves turn slimy and become food, so the packs keep feeding larvae well into winter.

How to notice it

  1. Find a shallow, slow-moving woodland brook from the bank, and look where leaves have piled up behind rocks, sticks, or in the gaps of a riffle.
  2. Crouch at the edge and watch the pile for a minute. Notice which leaves look slimy or skeletonized with holes and ragged edges.
  3. If an adult is with you, lift one handful of wet leaves into a white tray or pale bowl of stream water and wait for tiny larvae to move. Look for small wiggling bodies, or larvae wearing little tubes of sand or leaf bits.
  4. Tip everything gently back where you found it, in the same spot.

Try this with kids: Can you find a leaf with holes chewed in it, and a tiny animal that might have done the chewing?

Word to know: A “shredder” is an aquatic insect larva that feeds by chewing up leaves and other plant litter.

Safety

  • Children should stay with an adult at all times near moving water and keep to the bank or a spot where the water is ankle-deep at most.
  • Stream water in fall and winter is cold enough to numb hands and feet quickly; keep the visit short and have dry socks handy.
  • Banks are slippery with wet leaves, mud, and ice; do not step on ice over water, and skip the brook after heavy rain or when the water is high or fast.
  • Wash hands after touching stream water, and do not drink it.

Sources

  • leafpacknetwork.orgLeaf Pack Network (Stroud Water Research Center): 'The leaves accumulate behind the rocks forming natural leaf packs.' 'Shredders (which include crane flies, some caddiflies and stoneflies, sowbugs, and scuds) break the leaves down into fine particles by eating them.' Also: after a few weeks of submersion the leaves become slimy and in time are colonized by macroinvertebrates.
  • wav.extension.wisc.eduUniversity of Wisconsin Extension Water Action Volunteers: 'Leaf off (autumnal abscission) is a key seasonal event for streams'; craneflies and some stoneflies are shredders feeding on leaf material; leaves persist wedged between rocks; most of the same invertebrates are 'quite active in winter as well.'
  • northernwoodlands.orgNorthern Woodlands (New England), supporting only: stream insects overwinter as eggs, larvae or nymphs, and 'Many species hatch in time to consume autumn leaves and the bacteria that grow on them.'

Checked against these sources on September 29, 2026.

In the guide for November, December

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