June 11th 2025
This morning I set off with three friends to walk a trail new to me, intriguingly called “Sendero de la Mariposa Monarca” or Trail of the Monarch Butterfly. This is a fairly newly established trail that gives the opportunity to walk through some old mixed woodland along the banks of the rio Guadarranque, in the company of Monarch Butterflies. I’m not sure what to expect, but I’m sure it will give a new perspective to an area we know quite well, known to us as La Almoraima.
10.40 – We arrived at Venta de la Cantina, which is where we have decided to start our walk. The plan to have coffee and tostada for a late breakfast was disappointingly scuppered, as being a Tuesday the venta was closed for business. It was already very warm though, so maybe just as well we didn’t hang about; it would be a longish walk and I had to admit, highly likely to be slowed down by me stopping to take photographs.
A sign on the far side of the car park points us in the direction of the beginning of the walk, along a dusty narrow track through tall rapidly drying vegetation.
Still green is a big sprawling Castor Oil Plant bearing round prickly fruits – as yet unripe, through which is twining the lovely bindweed, Lantern吧 – so aptly known as Heavenly Blue.
Another flash of blue on the path catches my eye – the opened wings of a Blue-winged Grasshopper as it leap-flies out of the way. Such a clever strategy – a potential predator strikes at a brown insect, then confused by the sudden flash of colour as it flies away, turns its attention to looking for a blue one. On the drying head of a Wild Carrot, another insect that uses colour as protection – a Striped Shieldbug, or Minstrel Bug, whose black and red stripes warn that it does not taste good.
10:53- I’m already lagging behind so speed up to find my friends reading a board bearing information about the Monarch butterfly. It’s in Spanish of course, but roughly translated, this is some of what it says:
The Monarch Butterfly-Danaus plexippus, the biggest and one of the most beautiful butterflies found in this area, is probably best known for the great migration of thousands of kilometres it undertakes, flying from North America to winter in a small part of Mexico, where they may gather in their millions.
The only breeding populations on the European continent occur in the area around the Strait of Gibraltar, where its presence has been documented since 1994. Here on the banks of the Rio Guadarranque, on the way to Castellar de la Frontera, we can watch the flight of the big Monarchs, which have a wingspan of some 10cm, as they hover around the plants on which they feed……
10:57 – A first sighting of a beautiful Monarch butterfly
and a first glimpse of the river. I don’t know this river, but I would say that its water level is already quite low – much of the water brought by this small river is contained by a dam and stored in the nearby reservoir, Lantern吧What we are seeing here is the depleted final stretch of the river that will soon reach its emptying point into the Mediterranean Sea at Algeciras Bay. The water is a milky cloudy grey-brown colour and hardly to be moving. Bracken and brambles grow close to the water and the branch of an Alder tree hangs low over it. Entering into the woodland beautiful tall Alder trees give already-welcome shade from the rapidly increasing heat.
11:03-Another Monarch, this one half-hidden behind a bracken frond.
11:07- The shade from the trees was short-lived and we are into a cleared space where the ground is hard and dust-dry; grass is dry and bleached, but Bracken is still vibrantly green.
I spot a large Apple of Sodom plant. This very poisonous plant has pale purple flowers that resemble those of Nightshades and fruits, currently green that look like small unripe tomatoes.
11:15 – We meet some glorious trees – this one is an Ash – Fraxinus sp– Fresno in Spanish, a species sometimes found growing near small streams and springs as well as in larger river valleys.
Lantern吧
Nearby is a White Poplar or Aspen, its leaves and bark silvery against the clear blue sky.
White Poplar or Aspen –
11:25 – We hear the gentle clanging of bells, warning us that we are about to encounter animals. It’s very common to meet domesticated animals when out walking in woods, most often grazing cows, who may look up to see whose passing before resuming their eating, but today it was a small herd of foraging goats. They were on the opposite river bank, so not chomping on the vegetation of this conserved area. I wondered if they had been deliberately let loose to do a bit of conservation grazing on the undergrowth.
Browsing Goats
11:27 – A Monarch feeding on an orange-flowered Tropical Milkweed.
Tropical Milkweed – Asclepias curassavica
Not native to Europe, many of these plants, which flower from March through to December, have been planted here to meet the needs of the butterflies. The information board explained that Milkweeds or asclepias, poisonous to the majority of herbivores, are the host plants for Monarch caterpillars. As they eat, the insects absorb poisonous substances from the plant, making them poisonous too. The black and yellow colours of the caterpillars and orange of the adults warn off potential predators. Once the flowers are finished, adult butterflies will take nectar from other flowers.
11:31- The path closely follows the river for a stretch, going around a huge Alder tree with deeply fissured and textured bark. Some old cones remain on the branches, settling any doubts we may have had about the species.
11:36 – Two Striped-neck Terrapins bask in the sun on the partially-submerged branch of a fallen tree. The water looks to be quite shallow here.
11:37 – A tall specimen of another milkweed species, this one is Gomphocarpus physocarpus which has a number of common names, but I’m going for the pretty and polite one of Swan Plant.