Dave Hallock, Eldora. You see them on the tips of spruce tree branches, their brown coloration and hard structure almost looking like a cone. People have asked me about them for years, often thinking that they indicate something wrong with the tree. I have known they are a gall caused by insects and are harmless to the tree. But a recent article in Colorado Birds by famed retired Colorado State Forest Service entomologist David Leatherman opened up a new world of information about these common structures found on Colorado blue spruce and Engelmann spruce.

The galls are the work of the aphid-like insect Adelges cooley, commonly called the Cooley spruce gall aphid. Their life-cycle goes something like this. In late summer and fall, the aphids, which have most likely been feeding on the needles of Douglas-fir, fly to spruce where they overwinter at the base of needles. They emerge in spring and mature to adulthood, when females lay eggs on the underside of spruce twigs. The eggs hatch the same time spruce buds open. The hatched eggs begin to feed on the newly formed spruce needles - this wounds the needles at their base and the cluster of damaged needles will form into a cone-like gall. The galls contain chambers where the nymphs finish their development. The mature aphids exit the chambers in June or July and they disperse back to Douglas-fir or other spruce (if no fir around) and begin a new cycle. 

The coloration of the galls begins as green or purple. After they release the aphids, they turn brown. The spines on the galls are simply the tips of needles, the base of the cluster of needles has been modified into the gall chambers.

Who else knows about this cycle? Insect gleaning birds have been on to it for as long as they have co-habitated with the aphids. Ruby-crowned kinglets, mountain chickadees, white-breasted nuthatches, yellow-rumped warblers, brown creepers, pine siskins, downy woodpeckers, and dark-eyed juncos are some of the local species that take advantage of the abundance of aphids while searching the needles and branches of spruce and fir trees for insects. Dave Leatherman has observed broad-tailed hummingbirds catch flying aphids to bring back as food for their nestlings. 

While the brown Cooley galls we see on the tips of spruce branches have served their purpose for aphids, other insects will take up residence in the vacated chambers. And these are good places for our wintering birds to find food.

Nature happenings in May include the return of migratory bird species from the south, such as broad-tailed hummingbirds (some are back in late April), most flycatchers, violet-green swallows, house wrens, hermit thrushes, water pipits on the tundra, warbling vireos in aspen groves, yellow, MacGillivray’s and Wilson’s warblers along streams, Brewer’s blackbirds, brown-headed cowbirds, Western tanagers, black-headed grosbeaks, Green-tailed towhees, and vesper, chipping, white-crowned and Lincoln’s sparrows. Clark’s nutcrackers are nesting. Many other resident birds, including chickadees and nuthatches, may already be nesting, or at least in courtship or nest building stages.

Many mammals are migrating to higher elevations and some are having young. Elk that did not move to higher elevations in April will do so in May. This is the peak time for raccoons to give birth. Moose begin calving, with the optimal time being late May to early June. Coyotes and foxes may be giving birth or already caring for young. Chipmunks and ground squirrels should be fully emerged from winter dens. Mink are having young (beginning in late April). 

Small, dull brown, forest-dwelling butterflies can be common, including Western pine elfins and hoary elfins. The most common blue butterfly this month is the spring azure, while the most common white one is appropriately called the spring white.

Common flowers for May include pasque flowers (have even seen them blooming on the tundra as early as May 4), wild candytufts, spring beauties, and cut-leaf daisies. Chorus frogs may be heard calling around ponds and wetlands.  

(Note: Much of the information on Cooley Spruce Galls comes from the article “The Hungry Bird: Cooley Spruce Gall Adelgid” written by David Leatherman that appeared in the Fall 2020 issue of Colorado Birds)

(Originally published in the May 13, 2021, edition of The Mountain-Ear.)