Common butterwort -- Pinguicula vulgaris

Clambering over the steep rock wall at the head of a small drainage, we find ourselves on open terrain. We’re about one hundred feet high on a rocky peninsula jutting out into the lake. Ahead of us is the glacier with jagged peaks beyond, behind us a beaver-dammed lake and forest. There is a thin drizzle in the air, which seems right. At our feet is scarred rock, the deep grooves parallel to one another and most running toward the glacier. In these grooves, moss and water collect and out of them little plants with ornate flowers and sticky leaves, common butterwort (Pinguicula vulgaris).

Hearing Pinguicula, my mind is brought to Dracula. It’s a fun if slightly clunky rhyme, but there’s more than that. At first glance both appear familiar and unassuming figures, not obvious monsters. Common butterwort flowers are strikingly similar in shape and color to certain Viola, the ubiquitous and harmless “shrinking violet”. Similarly, in Bram Stoker’s novel the lawyer Jonathan Harker took the Count for an eccentric old man, English enlightenment blinding him to obvious warning signs of the supernatural around him. Look at the leaves, look at the teeth; something sinister hidden beneath. Pinguicula is no blood-sucking monster, though as a carnivorous plant it has to be ranked among the closest a plant can come.

Carnivorous plants are a set of species defined by their predation of small insects and tiny single-celled protozoa. Whereas most plants absorb required nutrients from soil, carnivorous plants supplement those soil nutrients through a brilliant and bizarre adaptation: preying upon insects which they capture, digest, and absorb. The mechanism of entrapment employed by these species is varied, each remarkable in its own way, but the reason for maintaining this lifestyle is universal. The common thread is a general lack of available nutrients in the soil where these plants grow. Added nutrition derived through predation, allows for the healthy growth of carnivorous plants in their nutrient poor home. While these plants are botanical anomalies, they are not really uncommon. There are at least 600 known carnivorous species found throughout the world in both tropical and temperate regions.

Like most carnivorous plants, common butterwort has an inherent conflict to resolve. On the one hand, they need insects to visit their flowers and pollinate in order to ensure the survival of the species. On the other hand, they need insects to land on their leaves and become food in order to ensure survival of the individual. It’s an interesting dilemma. How do they ensuring that some meet their end but enough escape to spread pollen? Different types of carnivorous plants have come up with different solutions, and common butterwort has two notable adaptations.

A solution across most carnivorous plant species is to physically separate the area of pollination from the area of consumption as much as possible. You often see long flower stalks and for common butterwort that rule holds true. By elevating the flowers high above the deadly basal rosettes, common butterwort reduces the probability that insects visiting their flowers will fall prey to their leaves.

The other, and more important, safeguard that common butterwort employs is the differentiation of pollinator insects and food insects, an attribute developed over time. The shape and size of a butterwort flower indicates that their primary pollinators are relatively large. The long nectar spurs of the flowers are the result of coevolution with insects capable of reaching deep inside to reach the small amount of sweet nectar on offer. These insects, typically butterflies, moths, and types of bees with long tongues, are far too large to get stuck on the leaves, easily escaping when they do happen to land on them. Luckily for common butterwort, the world is full of insects in all shapes and sizes. While common butterwort can rely on larger insects to pollinate, the hordes of gnats, midges and other small insects small enough to trap offer an abundance of potential prey.

The death offered to little insects by common butterwort is brutal and exposed. Most other carnivorous plants are decorous by comparison. Pitcherplants (Sarracenia) conceal their victims at the bottom of their deep pitchers, sundew (Drosera) leaves tend to coil up and partially cover trapped insects, and Venus flytrap (Dionaea muscipula) similarly cover over their prey between their extraordinary modified leaves. But common butterwort leaves, though low to the ground, openly flaunt their act.

The entire upper surface of a common butterwort leaf is covered in glistening droplets sitting atop tiny stalks. This substance, which makes the leaves look perpetually wet, is called mucilage and it is incredibly sticky. Any small insect attracted to the moisture or unlucky enough to land on the leaf is all but doomed. As it struggles to free itself, the insect becomes ever more coated in the sticky substance. The leaves have upward curled edges to ensure that the insect cannot roll off of the edge and to freedom. Fully coated and incapable of escape, the enzymes in the mucilage begin the work of breaking down the digestible parts of the insect which are then absorbed into the plant through small holes in the leaf. In the end, the indigestible husk of the insect is left in full view until winter comes and the leaves wither away.

Common butterwort has a strange and maybe unsurprising human application. Enzymes, which are used to curdle milk, are a key ingredient for making cheese, yogurt, and other dairy products. Rennet, the most commonly used source of these enzymes, is taken from the stomach of young ruminants. Because common butterwort leaves are essentially exposed stomachs, they too can be used in curdle milk. In Sweden, filmjölk is a variation of fermented milk which is popular under different names throughout the world. With a consistency somewhere in between yogurt and milk, it is a common breakfast food. Tätmjölk is a type of filmjölk which is made by placing Pinguicula leaves in milk and allowing it time to carry out the same chemical reaction the plant relays on to break down small insects. Given the abundance of common butterwort in the region and the expense of raising livestock, tätmjölk would have been the logical alternative for many Scandinavians.

I crouch down to take a closer look at this little colony of common butterwort that we have come across. The leaves are dotted with bugs and I see a few still trying to escape. I look up and around. It’s a big world and I think about how unlucky the little insects were to land here. I admire the plants too and think about the strange life they have carved out. These beautiful little monsters are having their cake and eating it too.