Life on Leaf Packs

By Kristen Travers, Water Quality Monitoring Coordinator

Hiking along the new birding trail at Middle Run Natural Area it’s hard not to gaze up at the glorious fall foliage.  As the trail meanders along the tributary of
White Clay Creek, leaves from the forest canopy flutter toward the ground.  I watch one leaf as it falls into the creek and begins to float downstream.  The leaf doesn’t float far until it becomes lodged in front of a large rock along with a clump of other leaves.  Looking along the creek other clumps of partly submerged leaves, called leaf packs, are scattered. 

A leaf pack in a small stream.

I reach under the water and grab a leaf pack that looks to have been in the water for a period of time – the tree leaves are covered in a slimy biofilm of fungi and bacteria that are beginning to decompose the leaves.  Slowly pulling the leaves apart reveals a hidden habitat for aquatic insects.    A large crane fly, a common leaf pack inhabitant this time of year, wriggles out from under a leaf.

Crane fly larvae (Family Tipulidae). Photo by: R. Heringslack

These strange looking insects spend most of their life under the water as larvae using the leaf packs as both a habitat as well as a food supply. Often referred to as shredders, crane flies, along with other aquatic insects that feed on tree leaves, provide an important ecosystem function shredding leaves into smaller pieces that then become food for other aquatic invertebrates.  After living about a year under the water, the larvae pupate and change into the terrestrial adults.  Adult crane flies, commonly seen during summer months, are often mistaken for large killer mosquitoes but fortunately are harmless.  They  may feed on nectar, if anything, as adults.

A face only a mother could love? Actually this view is the end of the abdomen – the two dots are spiracles used to obtain oxygen. The head of the crane fly is small and can be pulled back into the body rather like a turtle. Photo by: R. Heringslack

The next time that you’re out hiking near a stream, look for leaf packs – scoop up a handful of leaves, the slimier the better, and see what you can discover!  Help a stream – and a crane fly – by planting native trees or shrubs in your backyard or at a DNS tree planting event.  Native tree leaves provide a better quality food supply for our local aquatic and terrestrial insects.

Prize Alert:

What is the official aquatic macroinvertebrate of Delaware?

The first person to answer correctly will win the book Delaware’s Freshwater and Brackish-Water Fishes by Maynard Raasch.  Use the “Comments” section to submit your answer (press the little number below the date at the top to comment if you don’t see a comment form).

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