German conservation group warns against marbles in insect water trays

The Naturschutzbund Deutschland (NABU) cautions that placing glass marbles in garden insect water trays can create dangerous heat hazards. On hot, sunny days the marbles can become extremely hot, burning insects such as bees, bumblebees and butterflies that land on them and potentially causing deaths.

NABU recommends using shallow ceramic dishes and natural landing aids—stones, small twigs, moss or garden pebbles—that stay cool and provide safe access to water. The water should be refreshed daily, preferably with rainwater, and the tray should be positioned in a sunny, wind‑sheltered spot near flowering plants. Clean the dish with hot water only and avoid detergents that could harm insects.