A native pollinator explores an alien flower

These sand dunes, between Alnmouth and Warkworth, have long been a favourite destination for botanists. The hollows are filled with wild thyme, biting stonecrop, bird's foot trefoil, viper's bugloss and spotted, twayblade and pyramidal orchids, to name but a few. This is also one of the only places in our region where sea pea has been recorded - which I've searched for here but never found. But when we were there a couple of weeks ago, we did come across an interesting alien.

Our visit coincided with a mass emergence of five-spot burnet moths and when they were not busy producing the next generation they were swarming all over the flowers, notably ...

...... this garden iris, possibly Iris sibirica which someone must have planted here. Bearded iris, I. germanica, is recorded as an introduced alien here in George Swan's Flora of Northumberland, but this clearly isn't a bearded iris, which has a beard of hairs in the 'gullet' of the flower . It must have been here for quite a while and bore a couple of large, empty seed capsules from last year's flowers, so might seed itself around and establish a population. 

What was mos striking about the plant was what a magnet it was for the five-spot burnets. The plant is a bit of a beacon, being the tallest brightly-coloured object in the dunes, and they homed in on it from all around.

When they landed none of the moths seemed to have any idea how to feed on the plant's nectar, but they quite quickly worked out how to reach it.

Usually, like this one and the one below, they began by probing the petal surface with their proboscis ....

..

.... then, when they found that unrewarding, moved down to the petal base to reach the nectar.....

.... but after a while most seemed to align themselves with the yellow flash in the middle of the fall petal, which led them into the legitimate route to the nectar, used by the plant's natural pollinators which are bees.

This involved forcing their way into the confines of the tube between the fall petal and the standard petal above, which has the stamen concealed underneath it, so the visitor is forced to pick up pollen on its back.

Once the flower markings had pointed the burnet moth visitor in the right direction it invariably crawled all the way in - and became stuck, unable to reverse out. After a pause and a bit of a struggle the moths finally managed to force their way out through the narrow gap between fall and standard petals - and were always carrying iris pollen when they left.

The interesting aspect of this is that it's an example of a native pollinating insect responding correctly to the floral advertisements of an introduced, non-native flower species that is adapted to bee pollination and that the moths would not have encountered before or co-evolved with. The plants that the moths normally pollinate on the dunes have numerous small flowers with easily-accessible nectar. It's clear that these moths are pollinating the iris and most likely contributing to its seed set.